A Project Report On C Programming

A Project Report On C Programming

Submitted TO, Submitted By,
__________________ __________________ Grade: XII Date of Submission: __/__/____
Acknowledgement

I am very thankful to everyone who all supported me, for I have completed my project effectively and moreover, on time.

I am equally grateful to my computer teacher. He gave me moral support and guided me in different matters regarding the topic. He has been very kind and patient, whilst suggesting to me the outlines of this project, and correcting my doubts. I thank him for his overall support.

Last but not the least, I would like to thank my parents who helped me a lot in gathering different information, collecting data, paying the internet bills and guiding me from time to time in completing this project. Despite their busy schedules, they gave me different ideas to help make this project unique.

Thanking you,

XII– ‘A’

INTRODUCTION
C
Is a general-purpose, imperative computer programming language. It supports programming, lexical and recursion, while a static type system prevents many unintended operations. By design, C provides constructs that map efficiently to typical machine instructions, and therefore it has found lasting use in applications that had formerly been coded in assembly language, including operating systems as well as various application software for computers ranging from supercomputers to embedded systems.
C was originally developed by Dennis Ritchie between 1969 and 1973 at AT&T Bell Labs and used to (re-)implement the Unix operating system. It has since become one of the most widely used programming languages of all time, with C compilers from various vendors available for the majority of existing computer architectures and operating systems. C has been standardized by the American (ANSI) since 1989 (see ANSI C) and subsequently by the International Organization for Standardization (ISO).
Many later languages have borrowed directly or indirectly from C, including D, Go, Rust, Java, JavaScript, Limbo, LPC, C#,Objective-C, Perl, PHP, Python, Verilog (hardware description language), and Unix's C shell. These languages have drawn many of their control structures and other basic features from C, usually with overall syntactical similarity to C.
Design
C is an imperative (procedural) language. It was designed to be compiled using a relatively straightforward compiler, to provide low-level access to memory, to provide language constructs that map efficiently to machine instructions, and to require minimal run-time support. C was therefore useful for many applications that had formerly been coded in assembly, such as in system programming.
Despite its low-level capabilities, the language was designed to encourage cross-platform programming. A standards-compliant and portably written C program can be compiled for a very wide variety of computer platforms and operating systems with few changes to its source code. The language has become available on a very wide range of platforms, from embedded microcontrollers to supercomputers.

Overview
Like most imperative languages in the ALGOL tradition, C has facilities for structured programming and allows lexical variable scope and recursion, while a static type systemprevents many unintended operations. In C, all executable code is contained within subroutines, which are called "functions" (although not in the strict sense of functional programming). Function parameters are always passed by value. Pass-by-reference is simulated in C by explicitly passing pointer values. C program source text is free-format, using the semicolon as a statement terminator and curly braces for grouping blocks of statements.
The C language also exhibits the following characteristics:
There is a small, fixed number of keywords, including a full set of flow of control primitives: for, if/else, while, switch, and do/while. There is one namespace, and user-defined names are not distinguished from keywords by any kind of sigil.
There are a large number of arithmetical and logical operators, such as +, +=, ++, &, ~, etc.
More than one assignment may be performed in a single statement.
Function return values can be ignored when not needed.
Typing is static, but weakly enforced: all data has a type, but implicit conversions can be performed; for instance, characters can be used as integers.
Declaration syntax mimics usage context. C has no "define" keyword; instead, a statement beginning with the name of a type is taken as a declaration. There is no "function" keyword; instead, a function is indicated by the parentheses of an argument list.
User-defined (typedef) and compound types are possible.
Heterogeneous aggregate data types (struct) allow related data elements to be accessed and assigned as a unit.
Array indexing is a secondary notation, defined in terms of pointer arithmetic. Unlike structs, arrays are not first-class objects; they cannot be assigned or compared using single built-in operators. There is no "array" keyword, in use or definition; instead, square brackets indicate arrays syntactically, e.g. month
Enumerated types are possible with the enum keyword. They are not tagged, and are freely interconvertible with integers.
Strings are not a separate data type, but are conventionally implemented as null-terminated arrays of characters.
Low-level access to computer memory is possible by converting machine addresses to typed pointers.
Procedures (subroutines not returning values) are a special case of function, with an untyped return type void.
Functions may not be defined within the lexical scope of other functions.
Function and data pointers permit ad hoc run-time polymorphism.
A preprocessor performs macro definition, source code file inclusion, and conditional compilation.
There is a basic form of modularity: files can be compiled separately and linked together, with control over which functions and data objects are visible to other files viastatic and extern attributes.
Complex functionality such as I/O, string manipulation, and mathematical functions are consistently delegated to library routines.
C does not include some features found in newer, more modern high-level languages, including object orientation and garbage collection.
Relations to other languages
Many later languages have borrowed directly or indirectly from C, including C++, D, Go, Rust, Java, JavaScript, Limbo, LPC, C#, Objective-C, Perl, PHP, Python, Verilog(hardware description language),and Unix's C shell. These languages have drawn many of their control structures and other basic features from C. Most of them (with Python being the most dramatic exception) are also very syntactically similar to C in general, and they tend to combine the recognizable expression and statement syntax of C with underlying type systems, data models, and semantics that can be radically different.

History
Early developments

The origin of C is closely tied to the development of the Unix operating system, originally implemented in assembly language on a PDP-7by Ritchie and Thompson, incorporating several ideas from colleagues. Eventually they decided to port the operating system to a PDP-11. The original PDP-11 version of Unix was developed in assembly language. The developers were considering to rewrite the system using the B language, Thompson's simplified version of BCPL. However B's inability to take advantage of some of the PDP-11's features, notably byte addressability, led to the development of C.
The initial development of C occurred at AT&T Bell Labs between 1969 and 1973; according to Ritchie, the most creative period occurred in 1972. At that year a great part of Unix was rewritten in C By 1973, with the addition of struct types, the C language had become powerful enough that most of the Unix kernel was now in C.
Unix was one of the first operating system kernels implemented in a language other than assembly. (Earlier instances include the Multicssystem (written in PL/I), and MCP (Master Control Program) for the Burroughs B5000 written in ALGOL in 1961.) Circa 1977, further changes to the language were made by Ritchie and Stephen C. Johnson to facilitate portability of the Unix operating system. Johnson's Portable C Compiler served as the basis for several implementations of C on new platforms.
K&R C
In 1978, Brian Kernighan and Dennis Ritchie published the first edition of The C Programming Language. This book, known to C programmers as "K&R", served for many years as an informal specification of the language. The version of C that it describes is commonly referred to as K&R C. The second edition of the book covers the later ANSI C standard, described below.
K&R introduced several language features: standard I/O library long int data type unsigned int data type compound assignment operators of the form =op (such as =-) were changed to the form op= to remove the semantic ambiguity created by such constructs as i=-10, which had been interpreted as i =- 10 (decrement i by 10) instead of the possibly intended i = -10 (let i be -10)
Even after the publication of the 1989 ANSI standard, for many years K&R C was still considered the "lowest common denominator" to which C programmers restricted themselves when maximum portability was desired, since many older compilers were still in use, and because carefully written K&R C code can be legal Standard C as well.
In early versions of C, only functions that returned a non-int value needed to be declared if used before the function definition; a function used without any previous declaration was assumed to return type int, if its value was used.
For example: long some_function();
/* int */ other_function(); /* int */ calling_function()
{
long test1; register /* int */ test2; test1 = some_function(); if (test1 > 0) test2 = 0; else test2 = other_function(); return test2;
}
The int type specifiers which are commented out could be omitted in K&R C, but are required in later standards.
Since K&R function declarations did not include any information about function arguments, function parameter type checks were not performed, although some compilers would issue a warning message if a local function was called with the wrong number of arguments, or if multiple calls to an external function used different numbers or types of arguments. Separate tools such as Unix's lint utility were developed that (among other things) could check for consistency of function use across multiple source files.
In the years following the publication of K&R C, several features were added to the language, supported by compilers from AT&T (in particular PCC) and some other vendors. These included: void functions (i.e. functions with no return value) functions returning struct or union types (rather than pointers) assignment for struct data types
The large number of extensions and lack of agreement on a standard library, together with the language popularity and the fact that not even the Unix compilers precisely implemented the K&R specification, led to the necessity of standardization. programming code For print integer
#include <stdio.h> int main()
{
int a; printf("Enter an integer\n"); scanf("%d", &a); printf("Integer that you have entered is %d\n", a); return 0;
}
C program to check odd or even using modulus operator
#include<stdio.h>

main()
{
int n; printf("Enter an integer\n"); scanf("%d",&n); if ( n%2 == 0 ) printf("Even\n"); else printf("Odd\n"); return 0;
}
C programming code for LCM and HCF
#include <stdio.h> int main() { int a, b, x, y, t, gcd, lcm; printf("Enter two integers\n"); scanf("%d%d", &x, &y); a = x; b = y; while (b != 0) { t = b; b = a % b; a = t; } gcd = a; lcm = (x*y)/gcd; printf("Greatest common divisor of %d and %d = %d\n", x, y, gcd); printf("Least common multiple of %d and %d = %d\n", x, y, lcm); return 0;
}
Prime number program in c language
#include<stdio.h>

int main()
{
int n, i = 3, count, c; printf("Enter the number of prime numbers required\n"); scanf("%d",&n); if ( n >= 1 ) { printf("First %d prime numbers are :\n",n); printf("2\n"); } for ( count = 2 ; count <= n ; ) { for ( c = 2 ; c <= i - 1 ; c++ ) { if ( i%c == 0 ) break; } if ( c == i ) { printf("%d\n",i); count++; } i++; } return 0;
}
Palindrome number program c
#include <stdio.h> int main()
{
int n, reverse = 0, temp; printf("Enter a number to check if it is a palindrome or not\n"); scanf("%d",&n); temp = n; while( temp != 0 ) { reverse = reverse * 10; reverse = reverse + temp%10; temp = temp/10; } if ( n == reverse ) printf("%d is a palindrome number.\n", n); else printf("%d is not a palindrome number.\n", n); return 0;
}

C programming code for reverse words
#include <stdio.h> int main()
{
int n, reverse = 0; printf("Enter a number to reverse\n"); scanf("%d", &n); while (n != 0) { reverse = reverse * 10; reverse = reverse + n%10; n = n/10; } printf("Reverse of entered number is = %d\n", reverse); return 0;
}
C programming code for common mathematical problems
#include <stdio.h> int main()
{
int first, second, add, subtract, multiply; float divide; printf("Enter two integers\n"); scanf("%d%d", &first, &second); add = first + second; subtract = first - second; multiply = first * second; divide = first / (float)second; //typecasting printf("Sum = %d\n",add); printf("Difference = %d\n",subtract); printf("Multiplication = %d\n",multiply); printf("Division = %.2f\n",divide); return 0;
}
C programming code for Armstrong number
#include <stdio.h> int main()
{
int number, sum = 0, temp, remainder; printf("Enter an integer\n"); scanf("%d",&number); temp = number; while( temp != 0 ) { remainder = temp%10; sum = sum + remainder*remainder*remainder; temp = temp/10; } if ( number == sum ) printf("Entered number is an armstrong number.\n"); else printf("Entered number is not an armstrong number.\n"); return 0;
}

C programming code for addition using pointer
#include <stdio.h> int main()
{
int first, second, *p, *q, sum; printf("Enter two integers to add\n"); scanf("%d%d", &first, &second); p = &first; q = &second; sum = *p + *q; printf("Sum of entered numbers = %d\n",sum); return 0;
}
C programming code for leap year
#include <stdio.h> int main()
{
int year; printf("Enter a year to check if it is a leap year\n"); scanf("%d", &year); if ( year%400 == 0) printf("%d is a leap year.\n", year); else if ( year%100 == 0) printf("%d is not a leap year.\n", year); else if ( year%4 == 0 ) printf("%d is a leap year.\n", year); else printf("%d is not a leap year.\n", year); return 0;
}
C programming code to check vowels
#include <stdio.h> int main()
{
char ch; printf("Enter a character\n"); scanf("%c", &ch); if (ch == 'a' || ch == 'A' || ch == 'e' || ch == 'E' || ch == 'i' || ch == 'I' || ch =='o' || ch=='O' || ch == 'u' || ch == 'U') printf("%c is a vowel.\n", ch); else printf("%c is not a vowel.\n", ch); return 0;
}

C programming code to print the following * *** ***** *******
*********

#include <stdio.h> int main()
{
int row, c, n, temp; printf("Enter the number of rows in pyramid of stars you wish to see "); scanf("%d",&n); temp = n; for ( row = 1 ; row <= n ; row++ ) { for ( c = 1 ; c < temp ; c++ ) printf(" "); temp--; for ( c = 1 ; c <= 2*row - 1 ; c++ ) printf("*"); printf("\n"); } return 0;
}
Fibonacci series in c using for loop
/* Fibonacci Series c language */
#include<stdio.h>

int main()
{
int n, first = 0, second = 1, next, c; printf("Enter the number of terms\n"); scanf("%d",&n); printf("First %d terms of Fibonacci series are :-\n",n); for ( c = 0 ; c < n ; c++ ) { if ( c <= 1 ) next = c; else { next = first + second; first = second; second = next; } printf("%d\n",next); } return 0;
}
C programming code for transpose matrix
#include <stdio.h> int main()
{
int m, n, c, d, matrix[10][10], transpose[10][10]; printf("Enter the number of rows and columns of matrix "); scanf("%d%d",&m,&n); printf("Enter the elements of matrix \n"); for( c = 0 ; c < m ; c++ ) { for( d = 0 ; d < n ; d++ ) { scanf("%d",&matrix[c][d]); } } for( c = 0 ; c < m ; c++ ) { for( d = 0 ; d < n ; d++ ) { transpose[d][c] = matrix[c][d]; } } printf("Transpose of entered matrix :-\n"); for( c = 0 ; c < n ; c++ ) { for( d = 0 ; d < m ; d++ ) { printf("%d\t",transpose[c][d]); } printf("\n"); } return 0;
}

Code for finding maximum element in array
#include <stdio.h> int main()
{
int array[100], maximum, size, c, location = 1; printf("Enter the number of elements in array\n"); scanf("%d", &size); printf("Enter %d integers\n", size); for (c = 0; c < size; c++) scanf("%d", &array[c]); maximum = array[0]; for (c = 1; c < size; c++) { if (array[c] > maximum) { maximum = array[c]; location = c+1; } } printf("Maximum element is present at location %d and it's value is %d.\n", location, maximum); return 0;
}

ANSI C and ISO C
During the late 1970s and 1980s, versions of C were implemented for a wide variety of mainframe computers, minicomputers, and microcomputers, including the IBM PC, as its popularity began to increase significantly.
In 1983, the American National Standards Institute (ANSI) formed a committee, X3J11, to establish a standard specification of C. X3J11 based the C standard on the Unix implementation; however, the non-portable portion of the Unix C library was handed off to the IEEE working group 1003 to become the basis for the 1988 POSIX standard. In 1989, the C standard was ratified as ANSI X3.159-1989 "Programming Language C". This version of the language is often referred to as ANSI C, Standard C, or sometimes C89.
In 1990, the ANSI C standard (with formatting changes) was adopted by the International Organization for Standardization (ISO) as ISO/IEC 9899:1990, which is sometimes called C90. Therefore, the terms "C89" and "C90" refer to the same programming language.
ANSI, like other national standards bodies, no longer develops the C standard independently, but defers to the international C standard, maintained by the working group ISO/IEC JTC1/SC22/WG14. National adoption of an update to the international standard typically occurs within a year of ISO publication.
One of the aims of the C standardization process was to produce a superset of K&R C, incorporating many of the unofficial features subsequently introduced. The standards committee also included several additional features such as function prototypes (borrowed from C++), void pointers, support for international character sets and locales, and preprocessor enhancements. Although the syntax for parameter declarations was augmented to include the style used in C++, the K&R interface continued to be permitted, for compatibility with existing source code.
C89 is supported by current C compilers, and most C code being written today is based on it. Any program written only in Standard C and without any hardware-dependent assumptions will run correctly on any platform with a conforming C implementation, within its resource limits. Without such precautions, programs may compile only on a certain platform or with a particular compiler, due, for example, to the use of non-standard libraries, such as GUI libraries, or to a reliance on compiler- or platform-specific attributes such as the exact size of data types and byte endianness.
In cases where code must be compilable by either standard-conforming or K&R C-based compilers, the __STDC__ macro can be used to split the code into Standard and K&R sections to prevent the use on a K&R C-based compiler of features available only in Standard C.
After the ANSI/ISO standardization process, the C language specification remained relatively static for several years. In 1995 Normative Amendment 1 to the 1990 C standard (ISO/IEC 9899/AMD1:1995, known informally as C95) was published, to correct some details and to add more extensive support for international character sets.
C99
The C standard was further revised in the late 1990s, leading to the publication of ISO/IEC 9899:1999 in 1999, which is commonly referred to as "C99". It has since been amended three times by Technical Corrigenda
C99 introduced several new features, including inline functions, several new data types (including long long int and a complex type to represent complex numbers),variable-length arrays and flexible array members, improved support for IEEE 754 floating point, support for variadic macros (macros of variable arity), and support for one-line comments beginning with //, as in BCPL or C++. Many of these had already been implemented as extensions in several C compilers.
C99 is for the most part backward compatible with C90, but is stricter in some ways; in particular, a declaration that lacks a type specifier no longer has int implicitly assumed. A standard macro __STDC_VERSION__ is defined with value 199901L to indicate that C99 support is available. GCC, Solaris Studio, and other C compilers now support many or all of the new features of C99. The C compiler in Microsoft Visual C++, however, implements the C89 standard and those parts of C99 that are required for compatibility withC++11.
C11
In 2007, work began on another revision of the C standard, informally called "C1X" until its official publication on 2011-12-08. The C standards committee adopted guidelines to limit the adoption of new features that had not been tested by existing implementations.
The C11 standard adds numerous new features to C and the library, including type generic macros, anonymous structures, improved Unicode support, atomic operations, multi-threading, and bounds-checked functions. It also makes some portions of the existing C99 library optional, and improves compatibility with C++.
Embedded C
Historically, embedded C programming requires nonstandard extensions to the C language in order to support exotic features such as fixed-point arithmetic, multiple distinct memory banks, and basic I/O operations.
In 2008, the C Standards Committee published a technical report extending the C language to address these issues by providing a common standard for all implementations to adhere to. It includes a number of features not available in normal C, such as fixed-point arithmetic, named address spaces, and basic I/O hardware addressing.
Syntax
C has a formal grammar specified by the C standard Unlike languages such as FORTRAN 77, C source code is free-form which allows arbitrary use of whitespace to format code, rather than column-based or text-line-based restrictions. Comments may appear either between the delimiters /* and */, or (since C99) following // until the end of the line. Comments delimited by /* and */ do not nest, and these sequences of characters are not interpreted as comment delimiters if they appear inside string or character literals
C source files contain declarations and function definitions. Function definitions, in turn, contain declarations and statements. Declarations either define new types using keywords such as struct, union, and enum, or assign types to and perhaps reserve storage for new variables, usually by writing the type followed by the variable name. Keywords such as char and int specify built-in types. Sections of code are enclosed in braces ({ and }, sometimes called "curly brackets") to limit the scope of declarations and to act as a single statement for control structures.
As an imperative language, C uses statements to specify actions. The most common statement is an expression statement, consisting of an expression to be evaluated, followed by a semicolon; as a side effect of the evaluation, functions may be called and variables may be assigned new values. To modify the normal sequential execution of statements, C provides several control-flow statements identified by reserved keywords. Structured programming is supported by if(-else) conditional execution and by do-while,while, and for iterative execution (looping). The for statement has separate initialization, testing, and reinitialization expressions, any or all of which can be omitted.break and continue can be used to leave the innermost enclosing loop statement or skip to its reinitialization. There is also a non-structured goto statement which branches directly to the designated label within the function. switch selects a case to be executed based on the value of an integer expression.
Expressions can use a variety of built-in operators and may contain function calls. The order in which arguments to functions and operands to most operators are evaluated is unspecified. The evaluations may even be interleaved. However, all side effects (including storage to variables) will occur before the next "sequence point"; sequence points include the end of each expression statement, and the entry to and return from each function call. Sequence points also occur during evaluation of expressions containing certain operators (&&, ||, ?: and the comma operator). This permits a high degree of object code optimization by the compiler, but requires C programmers to take more care to obtain reliable results than is needed for other programming languages.
Kernighan and Ritchie say in the Introduction of The C Programming Language: "C, like any other language, has its blemishes. Some of the operators have the wrong precedence; some parts of the syntax could be better. The C standard did not attempt to correct many of these blemishes, because of the impact of such changes on already existing software.

Character set
The basic C source character set includes the following characters:
Lowercase and uppercase letters: a–z A–Z
Decimal digits: 0–9
Graphic characters: ! " # % & ' ( ) * + , - . / : ; < = > ? [ \ ] ^ _ { | } ~
Whitespace characters: space, horizontal tab, vertical tab, form feed, newline
Newline indicates the end of a text line; it need not correspond to an actual single character, although for convenience C treats it as one.
Additional multibyte encoded characters may be used in string literals, but they are not entirely portable. The latest C standard (C11) allows multinational Unicode characters to be embedded portably within C source text by using \uXXXX or \UXXXXXXXX encoding (where the X denotes a hexadecimal character), although this feature is not yet widely implemented.
The basic C execution character set contains the same characters, along with representations for alert, backspace, and carriage return. Run-time support for extended character sets has increased with each revision of the C standard.
C Programming Looping Constructs
Computers are very good at performing repetitive tasks very quickly. In this section we will learn how to make computer repeat actions either a specified number of times or until some stopping condition is met.
While Loops ( Condition-Controlled Loops )
Both while loops and do-while loops ( see below ) are condition-controlled, meaning that they continue to loop until some condition is met.
Both while and do-while loops alternate between performing actions and testing for the stopping condition.
While loops check for the stopping condition first, and may not execute the body of the loop at all if the condition is initially false.
Syntax:
while( condition ) body; where the body can be either a single statement or a block of statements within { curly braces }.
Example:
int i = 0; while( i < 5 ) printf( "i = %d\n", i++ ); printf( "After loop, i = %d\n", i );
Do-while Loops do-while loops are exactly like while loops, except that the test is performed at the end of the loop rather than the beginning.
This guarantees that the loop will be performed at least once, which is useful for checking user input among other things ( see example below. )
Syntax:
do { body; } while( condition );
In theory the body can be either a single statement or a block of statements within { curly braces }, but in practice the curly braces are almost always used with do-whiles.
Example:
int month; do { printf( "Please enter the month of your birth > " ); scanf( "%d", &month ); } while ( month < 1 || month > 12 );
Note that the above example could be improved by reporting to the user what the problem is if month is not in the range 1 to 12, and that it could also be done using a while loop if month were initialized to a value that ensures entering the loop.
The following diagram shows the difference between while and do-while loops. Note that once you enter the loop, the operation is identical from that point forward:
Introduction to C Programming Arrays
Overview
An array is a collection of data items, all of the same type, accessed using a common name.
A one-dimensional array is like a list; A two dimensional array is like a table; The C language places no limits on the number of dimensions in an array, though specific implementations may.
Some texts refer to one-dimensional arrays as vectors, two-dimensional arrays as matrices, and use the general term arrays when the number of dimensions is unspecified or unimportant.
Declaring Arrays
Array variables are declared identically to variables of their data type, except that the variable name is followed by one pair of square [ ] brackets for each dimension of the array.
Uninitialized arrays must have the dimensions of their rows, columns, etc. listed within the square brackets.
Dimensions used when declaring arrays in C must be positive integral constants or constant expressions.
In C99, dimensions must still be positive integers, but variables can be used, so long as the variable has a positive value at the time the array is declared. ( Space is allocated only once, at the time the array is declared. The array does NOT change sizes later if the variable used to declare it changes. )
Examples:
int i, j, intArray[ 10 ], number; float floatArray[ 1000 ]; int tableArray[ 3 ][ 5 ]; /* 3 rows by 5 columns */ const int NROWS = 100; // ( Old code would use #define NROWS 100 ) const int NCOLS = 200; // ( Old code would use #define NCOLS 200 ) float matrix[ NROWS ][ NCOLS ];
C99 Only Example: int numElements; printf( "How big an array do you want? " ); scanf( "%d", &numElements; ) if( numElements <= 0 ) { printf( "Error - Quitting\n" ); exit( 0 ); } double data[ numElements ]; // This only works in C99, not in plain C
Initializing Arrays
Arrays may be initialized when they are declared, just as any other variables.
Place the initialization data in curly {} braces following the equals sign. Note the use of commas in the examples below.
An array may be partially initialized, by providing fewer data items than the size of the array. The remaining array elements will be automatically initialized to zero.
If an array is to be completely initialized, the dimension of the array is not required. The compiler will automatically size the array to fit the initialized data. ( Variation: Multidimensional arrays - see below. )
Examples:
int i = 5, intArray[ 6 ] = { 1, 2, 3, 4, 5, 6 }, k; float sum = 0.0f, floatArray[ 100 ] = { 1.0f, 5.0f, 20.0f }; double piFractions[ ] = { 3.141592654, 1.570796327, 0.785398163 };
Designated Initializers:
In C99 there is an alternate mechanism, that allows you to initialize specific elements, not necessarily at the beginning.
This method can be mixed in with traditional iniitalization
For example: int numbers[ 100 ] = { 1, 2, 3, [10] = 10, 11, 12, [60] = 50, [42] = 420 };
In this example,the first three elements are initialized to 1, 2, and 3 respectively.
Then element 10 ( the 11th element ) is initialized to 10
The next two elements ( 12th and 13th ) are initialized to 11 and 12 respectively.
Element number 60 ( the 61st ) is initialized to 50, and number 42 ( the 43rd ) to 420.
( Note that the designated initializers do not need to appear in order. )
As with traditional methods, all uninitialized values are set to zero.
If the size of the array is not given, then the largest initialized position determines the size of the array. Using Arrays
Elements of an array are accessed by specifying the index ( offset ) of the desired element within square [ ] brackets after the array name.
Array subscripts must be of integer type. ( int, long int, char, etc. )
VERY IMPORTANT: Array indices start at zero in C, and go to one less than the size of the array. For example, a five element array will have indices zero through four. This is because the index in C is actually an offset from the beginning of the array. ( The first element is at the beginning of the array, and hence has zero offset. )
Landmine: The most common mistake when working with arrays in C is forgetting that indices start at zero and stop one less than the array size.
Arrays are commonly used in conjunction with loops, in order to perform the same calculations on all ( or some part ) of the data items in the array.
Sample Programs Using 1-D Arrays
The first sample program uses loops and arrays to calculate the first twenty Fibonacci numbers. Fibonacci numbers are used to determine the sample points used in certain optimization methods. /* Program to calculate the first 20 Fibonacci numbers. */ #include <stdlib.h> #include <stdio.h>

int main( void ) { int i, fibonacci[ 20 ]; fibonacci[ 0 ] = 0; fibonacci[ 1 ] = 1; for( i = 2; i < 20; i++ ) fibonacci[ i ] = fibonacci[ i - 2 ] + fibonacci[ i - 1 ]; for( i = 0; i < 20; i++ ) printf( "Fibonacci[ %d ] = %f\n", i, fibonacci[ i ] ); } /* End of sample program to calculate Fibonacci numbers */ What is the output of the following program: /* Sample Program Using Arrays */ #include <stdlib.h> #include <stdio.h> int main( void ) { int numbers[ 10 ]; int i, index = 2; for( i = 0; i < 10; i++ ) numbers[ i ] = i * 10; numbers[ 8 ] = 25; numbers[ 5 ] = numbers[ 9 ] / 3; numbers[ 4 ] += numbers[ 2 ] / numbers[ 1 ]; numbers[ index ] = 5; ++numbers[ index ]; numbers[ numbers[ index++ ] ] = 100; numbers[ index ] = numbers[ numbers[ index + 1 ] / 7 ]--; for( index = 0; index < 10; index++ ) printf( "numbers[ %d ] = %d\n" index, numbers[ index ] ); } /* End of second sample program */

Multidimensional Arrays
Multi-dimensional arrays are declared by providing more than one set of square [ ] brackets after the variable name in the declaration statement.
One dimensional arrays do not require the dimension to be given if the array is to be completely initialized. By analogy, multi-dimensional arrays do not require the firstdimension to be given if the array is to be completely initialized. All dimensions after the first must be given in any case.
For two dimensional arrays, the first dimension is commonly considered to be the number of rows, and the second dimension the number of columns. We will use this convention when discussing two dimensional arrays.
Two dimensional arrays are considered by C/C++ to be an array of ( single dimensional arrays ). For example, "int numbers[ 5 ][ 6 ]" would refer to a single dimensional array of 5 elements, wherein each element is a single dimensional array of 6 integers. By extension, "int numbers[ 12 ][ 5 ][ 6 ]" would refer to an array of twelve elements, each of which is a two dimensional array, and so on.
Another way of looking at this is that C stores two dimensional arrays by rows, with all elements of a row being stored together as a single unit. Knowing this can sometimes lead to more efficient programs.
Multidimensional arrays may be completely initialized by listing all data elements within a single pair of curly {} braces, as with single dimensional arrays.
It is better programming practice to enclose each row within a separate subset of curly {} braces, to make the program more readable. This is required if any row other than the last is to be partially initialized. When subsets of braces are used, the last item within braces is not followed by a comma, but the subsets are themselves separated by commas.
Multidimensional arrays may be partially initialized by not providing complete initialization data. Individual rows of a multidimensional array may be partially initialized, provided that subset braces are used.
Individual data items in a multidimensional array are accessed by fully qualifying an array element. Alternatively, a smaller dimensional array may be accessed by partially qualifying the array name. For example, if "data" has been declared as a three dimensional array of floats, then data[ 1 ][ 2 ][ 5 ] would refer to a float, data[ 1 ][ 2 ] would refer to a one-dimensional array of floats, and data[ 1 ] would refer to a two-dimensional array of floats. The reasons for this and the incentive to do this relate to memory-management issues that are beyond the scope of these notes.
Sample Program Using 2-D Arrays /* Sample program Using 2-D Arrays */ #include <stdlib.h> #include <stdio.h> int main( void ) { /* Program to add two multidimensional arrays */ /* Written May 1995 by George P. Burdell */ int a[ 2 ][ 3 ] = { { 5, 6, 7 }, { 10, 20, 30 } }; int b[ 2 ][ 3 ] = { { 1, 2, 3 }, { 3, 2, 1 } }; int sum[ 2 ][ 3 ], row, column; /* First the addition */ for( row = 0; row < 2; row++ ) for( column = 0; column < 3; column++ ) sum[ row ][ column ] = a[ row ][ column ] + b[ row ][ column ]; /* Then print the results */ printf( "The sum is: \n\n" ); for( row = 0; row < 2; row++ ) { for( column = 0; column < 3; column++ ) printf( "\t%d", sum[ row ][ column ] ); printf( '\n' ); /* at end of each row */ } return 0; }
Pointers
Pointers are often thought to be the most difficult aspect of C. It's true that many people have various problems with pointers, and that many programs founder on pointer-related bugs. Actually, though, many of the problems are not so much with the pointers per se but rather with the memory they point to, and more specifically, when there isn't any valid memory which they point to. As long as you're careful to ensure that the pointers in your programs always point to valid memory, pointers can be useful, powerful, and relatively trouble-free tools. (We'll talk about memory allocation in the next chapter.)
[This chapter is the only one in this series that contains any graphics. If you are using a text-only browser, there are a few figures you won't be able to see.]
A pointer is a variable that points at, or refers to, another variable. That is, if we have a pointer variable of type ``pointer to int,`` it might point to the int variable i, or to the third cell of the int array a. Given a pointer variable, we can ask questions like, ``What's the value of the variable that this pointer points to?''
Why would we want to have a variable that refers to another variable? Why not just use that other variable directly? The answer is that a level of indirection can be very useful. (Indirection is just another word for the situation when one variable refers to another.)
C supports the use of pointers, a type of reference that records the address or location of an object or function in memory. Pointers can be dereferenced to access data stored at the address pointed to, or to invoke a pointed-to function. Pointers can be manipulated using assignment or pointer arithmetic. The run-time representation of a pointer value is typically a raw memory address (perhaps augmented by an offset-within-word field), but since a pointer's type includes the type of the thing pointed to, expressions including pointers can be type-checked at compile time. Pointer arithmetic is automatically scaled by the size of the pointed-to data type. Pointers are used for many different purposes in C. Text strings are commonly manipulated using pointers into arrays of characters. Dynamic memory allocation is performed using pointers. Many data types, such as trees, are commonly implemented as dynamically allocated struct objects linked together using pointers. Pointers to functions are useful for passing functions as arguments to higher-order functions (such as qsort or bsearch) or as callbacks to be invoked by event handlers
A null pointer value explicitly points to no valid location. Dereferencing a null pointer value is undefined, often resulting in a segmentation fault. Null pointer values are useful for indicating special cases such as no "next" pointer in the final node of a linked list, or as an error indication from functions returning pointers. In appropriate contexts in source code, such as for assigning to a pointer variable, a null pointer constant can be written as 0, with or without explicit casting to a pointer type, or as the NULL macro defined by several standard headers. In conditional contexts, null pointer values evaluate to false, while all other pointer values evaluate to true.
Void pointers (void *) point to objects of unspecified type, and can therefore be used as "generic" data pointers. Since the size and type of the pointed-to object is not known, void pointers cannot be dereferenced, nor is pointer arithmetic on them allowed, although they can easily be (and in many contexts implicitly are) converted to and from any other object pointer type
Careless use of pointers is potentially dangerous. Because they are typically unchecked, a pointer variable can be made to point to any arbitrary location, which can cause undesirable effects. Although properly used pointers point to safe places, they can be made to point to unsafe places by using invalid pointer arithmetic; the objects they point to may be deallocated and reused (dangling pointers); they may be used without having been initialized (wild pointers); or they may be directly assigned an unsafe value using a cast, union, or through another corrupt pointer. In general, C is permissive in allowing manipulation of and conversion between pointer types, although compilers typically provide options for various levels of checking. Some other programming languages address these problems by using more restrictive reference types.

Imagine a club which elects new officers each year. In its clubroom, it might have a set of mailboxes for each member, along with special mailboxes for the president, secretary, and treasurer. The bank doesn't mail statements to the treasurer under the treasurer's name; it mails them to ``treasurer,'' and the statements go to the mailbox marked ``treasurer.'' This way, the bank doesn't have to change the mailing address it uses every year. The mailboxes labeled ``president,'' ``treasurer,'' and ``secretary'' are a little bit like pointers--they don't refer to people directly.
If we make the analogy that a mailbox holding letters is like a variable holding numbers, then mailboxes for the president, secretary, and treasurer aren't quite like pointers, because they're still mailboxes which in principle could hold letters directly. But suppose that mail is never actually put in those three mailboxes: suppose each of the officers' mailboxes contains a little marker listing the name of the member currently holding that office. When you're sorting mail, and you have a letter for the treasurer, you first go to the treasurer's mailbox, but rather than putting the letter there, you read the name on the marker there, and put the mail in the mailbox for that person. Similarly, if the club is poorly organized, and the treasurer stops doing his job, and you're the president, and one day you get a call from the bank saying that the club's account is in arrears and the treasurer hasn't done anything about it and asking if you, the president, can look into it; and if the club is so poorly organized that you've forgotten who the treasurer is, you can go to the treasurer's mailbox, read the name on the marker there, and go to that mailbox (which is probably overflowing) to find all the treasury-related mail.
We could say that the markers in the mailboxes for the president, secretary, and treasurer were pointers to other mailboxes. In an analogous way, pointer variables in C contain pointers to other variables or memory locations.
Memory Allocation
In this chapter, we'll meet malloc, C's dynamic memory allocation function, and we'll cover dynamic memory allocation in some detail.
As we begin doing dynamic memory allocation, we'll begin to see (if we haven't seen it already) what pointers can really be good for. Many of the pointer examples in the previous chapter (those which used pointers to access arrays) didn't do all that much for us that we couldn't have done using arrays. However, when we begin doing dynamic memory allocation, pointers are the only way to go, because what malloc returns is a pointer to the memory it gives us. (Due to the equivalence between pointers and arrays, though, we will still be able to think of dynamically allocated regions of storage as if they were arrays, and even to use array-like subscripting notation on them.)
You have to be careful with dynamic memory allocation. malloc operates at a pretty ``low level''; you will often find yourself having to do a certain amount of work to manage the memory it gives you. If you don't keep accurate track of the memory which malloc has given you, and the pointers of yours which point to it, it's all too easy to accidentally use a pointer which points ``nowhere'', with generally unpleasant results. (The basic problem is that if you assign a value to the location pointed to by a pointer: *p = 0; and if the pointer p points ``nowhere'', well actually it can be construed to point somewhere, just not where you wanted it to, and that ``somewhere'' is where the 0 gets written. If the ``somewhere'' is memory which is in use by some other part of your program, or even worse, if the operating system has not protected itself from you and ``somewhere'' is in fact in use by the operating system, things could get ugly.)

Keywords
C89 has 32 keywords (reserved words with special meaning): auto break case char const continue default do double else enum extern float for goto if int long register return short signed sizeof static struct switch typedef union unsigned void volatile while
C99 adds five more keywords:
_Bool
_Complex
_Imaginary
inline restrict C11 adds seven more keywords:
_Alignas
_Alignof
_Atomic
_Generic
_Noreturn
_Static_assert

Most of the recently added keywords begin with an underscore followed by a capital letter, because identifiers of that form were previously reserved by the C standard for use only by implementations. Since existing program source code should not have been using these identifiers, it would not be affected when C implementations started supporting these extensions to the programming language. Some standard headers do define more convenient synonyms for underscored identifiers. The language previously included a reserved keyword called entry, but this was never implemented, and has now been removed as a reserved word.

Operators
Main article: Operators in C and C++
C supports a rich set of operators, which are symbols used within an expression to specify the manipulations to be performed while evaluating that expression. C has operators for: arithmetic: +, -, *, /, % assignment: = augmented assignment: +=, -=, *=, /=, %=, &=, |=, ^=, <<=, >>= bitwise logic: ~, &, |, ^ bitwise shifts: <<, >> boolean logic: !, &&, || conditional evaluation: ? : equality testing: ==, != calling functions: ( ) increment and decrement: ++, -- member selection: ., -> object size: sizeof order relations: <, <=, >, >= reference and dereference: &, *, [ ] sequencing: , subexpression grouping: ( ) type conversion: (typename)
C uses the = operator, reserved in mathematics to express equality, to indicate assignment, following the precedent of Fortran and PL/I, but unlike ALGOL and its derivatives. The similarity between C's operator for assignment and that for equality (==) has been criticised as it makes it easy to accidentally substitute one for the other. In many cases, each may be used in the context of the other without a compilation error (although some compilers produce warnings). For example, the conditional expression in if(a=b+1) is true if a is not zero after the assignment. Additionally, C's operator precedence is non-intuitive, such as == binding more tightly than & and | in expressions like x & 1 == 0, which would need to be written (x & 1) == 0 to be properly evaluated
"Hello, world" example
The "hello, world" example, which appeared in the first edition of K&R, has become the model for an introductory program in most programming textbooks, regardless of programming language. The program prints "hello, world" to the standard output, which is usually a terminal or screen display.
The original version was: main() { printf("hello, world\n");
}
A standard-conforming "hello, world" program is:
#include <stdio.h> int main(void)
{
printf("hello, world\n");
}
The first line of the program contains a preprocessing directive, indicated by #include. This causes the compiler to replace that line with the entire text of the stdio.hstandard header, which contains declarations for standard input and output functions such as printf. The angle brackets surrounding stdio.h indicate that stdio.h is located using a search strategy that prefers headers in the compiler's include path to other headers having the same name; double quotes are used to include local or project-specific header files.
The next line indicates that a function named main is being defined. The main function serves a special purpose in C programs; the run-time environment calls the mainfunction to begin program execution. The type specifier int indicates that the value that is returned to the invoker (in this case the run-time environment) as a result of evaluating the main function, is an integer. The keyword void as a parameter list indicates that this function takes no arguments
The opening curly brace indicates the beginning of the definition of the main function.
The next line calls (diverts execution to) a function named printf, which is supplied from a system library. In this call, the printf function is passed (provided with) a single argument, the address of the first character in the string literal "hello, world\n". The string literal is an unnamed array with elements of type char, set up automatically by the compiler with a final 0-valued character to mark the end of the array (printf needs to know this). The \n is an escape sequence that C translates to a newline character, which on output signifies the end of the current line. The return value of the printf function is of type int, but it is silently discarded since it is not used. (A more careful program might test the return value to determine whether or not the printf function succeeded.) The semicolon ; terminates the statement.
The closing curly brace indicates the end of the code for the main function. According to the C99 specification and newer, main function will implicitly return a status of 0upon reaching the } that terminates the function. This is interpreted by the run-time system as an exit code indicating successful execution
Data types
C has a static weak typing type system that shares some similarities with that of ALGOL descendants such as Pascal. According to Feuer, C is not an Algol descendent. There are built-in types for integers of various sizes, both signed and unsigned, floating-point numbers, characters, and enumerated types (enum). C99 added a boolean datatype. There are also derived types including arrays, pointers, records (struct), and untagged unions (union).
C is often used in low-level systems programming where escapes from the type system may be necessary. The compiler attempts to ensure type correctness of most expressions, but the programmer can override the checks in various ways, either by using a type cast to explicitly convert a value from one type to another, or by using pointers or unions to reinterpret the underlying bits of a data object in some other way.
Some find C's declaration syntax unintuitive, particularly for function pointers. (Ritchie's idea was to declare identifiers in contexts resembling their use: "declaration reflects use".
C's usual arithmetic conversions allow for efficient code to be generated, but can sometimes produce unexpected results. For example, a comparison of signed and unsigned integers of equal width requires a conversion of the signed value to unsigned. This can generate unexpected results if the signed value is negative.

Arrays
Array types in C are traditionally of a fixed, static size specified at compile time. (The more recent C99 standard also allows a form of variable-length arrays.) However, it is also possible to allocate a block of memory (of arbitrary size) at run-time, using the standard library's malloc function, and treat it as an array. C's unification of arrays and pointers means that declared arrays and these dynamically allocated simulated arrays are virtually interchangeable.
Since arrays are always accessed (in effect) via pointers, array accesses are typically not checked against the underlying array size, although some compilers may providebounds checking as an option. Array bounds violations are therefore possible and rather common in carelessly written code, and can lead to various repercussions, including illegal memory accesses, corruption of data, buffer overruns, and run-time exceptions. If bounds checking is desired, it must be done manually.
C does not have a special provision for declaring multidimensional arrays, but rather relies on recursion within the type system to declare arrays of arrays, which effectively accomplishes the same thing. The index values of the resulting "multidimensional array" can be thought of as increasing in row-major order.
Multidimensional arrays are commonly used in numerical algorithms (mainly from applied linear algebra) to store matrices. The structure of the C array is well suited to this particular task. However, since arrays are passed merely as pointers, the bounds of the array must be known fixed values or else explicitly passed to any subroutine that requires them, and dynamically sized arrays of arrays cannot be accessed using double indexing. (A workaround for this is to allocate the array with an additional "row vector" of pointers to the columns.)
C99 introduced "variable-length arrays" which address some, but not all, of the issues with ordinary C arrays.
Array–pointer interchange ability
The subscript notation x[i] (where x designates a pointer) is a syntactic sugar for *(x+i).[29] Taking advantage of the compiler's knowledge of the pointer type, the address that x + i points to is not the base address (pointed to by x) incremented by i bytes, but rather is defined to be the base address incremented by i multiplied by the size of an element that x points to. Thus, x[i] designates the i+1th element of the array.
Furthermore, in most expression contexts (a notable exception is as operand of sizeof), the name of an array is automatically converted to a pointer to the array's first element. This implies that an array is never copied as a whole when named as an argument to a function, but rather only the address of its first element is passed. Therefore, although function calls in C use pass-by-value semantics, arrays are in effect passed by reference.
The size of an element can be determined by applying the operator sizeof to any dereferenced element of x, as in n = sizeof *x or n = sizeof x[0], and the number of elements in a declared array A can be determined as sizeof A / sizeof A[0]. The latter only applies to array names: variables declared with subscripts (int A[20]). Due to the semantics of C, it is not possible to determine the entire size of arrays through pointers to arrays or those created by dynamic allocation (malloc); code such assizeof arr / sizeof arr[0] (where arr = A designates a pointer) will not work since the compiler assumes the size of the pointer itself is being requested. Since array name arguments to sizeof are not converted to pointers, they do not exhibit such ambiguity. However, arrays created by dynamic allocation are initialized to pointers rather than true array variables, so they suffer from the same sizeof issues as array pointers.
Thus, despite this apparent equivalence between array and pointer variables, there is still a distinction to be made between them. Even though the name of an array is, in most expression contexts, converted into a pointer (to its first element), this pointer does not itself occupy any storage; the array name is not an l-value, and its address is a constant, unlike a pointer variable. Consequently, what an array "points to" cannot be changed, and it is impossible to assign a new address to an array name. Array contents may be copied, however, by using the memcpy function, or by accessing the individual elements.
Memory management
One of the most important functions of a programming language is to provide facilities for managing memory and the objects that are stored in memory. C provides three distinct ways to allocate memory for objects:
Static memory allocation: space for the object is provided in the binary at compile-time; these objects have an extent (or lifetime) as long as the binary which contains them is loaded into memory.
Automatic memory allocation: temporary objects can be stored on the stack, and this space is automatically freed and reusable after the block in which they are declared is exited.
Dynamic memory allocation: blocks of memory of arbitrary size can be requested at run-time using library functions such as malloc from a region of memory called theheap; these blocks persist until subsequently freed for reuse by calling the library function realloc or free
These three approaches are appropriate in different situations and have various tradeoffs. For example, static memory allocation has little allocation overhead, automatic allocation may involve slightly more overhead, and dynamic memory allocation can potentially have a great deal of overhead for both allocation and deal location. The persistent nature of static objects is useful for maintaining state information across function calls, automatic allocation is easy to use but stack space is typically much more limited and transient than either static memory or heap space, and dynamic memory allocation allows convenient allocation of objects whose size is known only at run-time. Most C programs make extensive use of all three.
Where possible, automatic or static allocation is usually simplest because the storage is managed by the compiler, freeing the programmer of the potentially error-prone chore of manually allocating and releasing storage. However, many data structures can change in size at runtime, and since static allocations (and automatic allocations before C99) must have a fixed size at compile-time, there are many situations in which dynamic allocation is necessary. Prior to the C99 standard, variable-sized arrays were a common example of this. (See the article on malloc for an example of dynamically allocated arrays.) Unlike automatic allocation, which can fail at run time with uncontrolled consequences, the dynamic allocation functions return an indication (in the form of a null pointer value) when the required storage cannot be allocated. (Static allocation that is too large is usually detected by the linker or loader, before the program can even begin execution.)
Unless otherwise specified, static objects contain zero or null pointer values upon program startup. Automatically and dynamically allocated objects are initialized only if an initial value is explicitly specified; otherwise they initially have indeterminate values (typically, whatever bit pattern happens to be present in the storage, which might not even represent a valid value for that type). If the program attempts to access an uninitialized value, the results are undefined. Many modern compilers try to detect and warn about this problem, but both false positives and false negatives can occur.
Another issue is that heap memory allocation has to be synchronized with its actual usage in any program in order for it to be reused as much as possible. For example, if the only pointer to a heap memory allocation goes out of scope or has its value overwritten before free() is called, then that memory cannot be recovered for later reuse and is essentially lost to the program, a phenomenon known as a memory leak. Conversely, it is possible for memory to be freed but continue to be referenced, leading to unpredictable results. Typically, the symptoms will appear in a portion of the program far removed from the actual error, making it difficult to track down the problem. (Such issues are ameliorated in languages with automatic garbage collection.)
Libraries
The C programming language uses libraries as its primary method of extension. In C, a library is a set of functions contained within a single "archive" file. Each library typically has a header file, which contains the prototypes of the functions contained within the library that may be used by a program, and declarations of special data types and macro symbols used with these functions. In order for a program to use a library, it must include the library's header file, and the library must be linked with the program, which in many cases requires compiler flags (e.g., -lm, shorthand for "math library").[25]
The most common C library is the C standard library, which is specified by the ISO and ANSI C standards and comes with every C implementation. (Implementations which target limited environments such as embedded systems may provide only a subset of the standard library.) This library supports stream input and output, memory allocation, mathematics, character strings, and time values. Several separate standard headers (for example, stdio.h) specify the interfaces for these and other standard library facilities.
Another common set of C library functions are those used by applications specifically targeted for Unix and Unix-like systems, especially functions which provide an interface to the kernel. These functions are detailed in various standards such as POSIX and the Single UNIX Specification.
Since many programs have been written in C, there are a wide variety of other libraries available. Libraries are often written in C because C compilers generate efficient object code; programmers then create interfaces to the library so that the routines can be used from higher-level languages like Java, Perl, and Python
Language tools
Tools have been created to help C programmers avoid some of the problems inherent in the language, such as statements with undefined behavior or statements that are not a good practice because they are likely to result in unintended behavior or run-time errors.
Automated source code checking and auditing are beneficial in any language, and for C many such tools exist, such as Lint. A common practice is to use Lint to detect questionable code when a program is first written. Once a program passes Lint, it is then compiled using the C compiler. Also, many compilers can optionally warn about syntactically valid constructs that are likely to actually be errors. MISRA C is a proprietary set of guidelines to avoid such questionable code, developed for embedded systems.
There are also compilers, libraries, and operating system level mechanisms for performing actions that are not a standard part of C, such as array bounds checking, buffer overflow detection, serialization, and automatic garbage collection.
Tools such as Purify or Valgrind and linking with libraries containing special versions of the memory allocation functions can help uncover runtime errors in memory usage.
Uses
C is often used for "system programming", including implementing operating systems and embedded system applications, due to a combination of desirable characteristics such as code portability and efficiency, ability to access specific hardware addresses, ability to pun types to match externally imposed data access requirements, and low run-timedemand on system resources. C can also be used for website programming using CGI as a "gateway" for information between the Web application, the server, and the browser Some reasons for choosing C over interpreted languages are its speed, stability, and near-universal availability
One consequence of C's wide availability and efficiency is that compilers, libraries, and interpreters of other programming languages are often implemented in C. The primary implementations of Python (CPython), Perl 5, and PHP are all written in C.
Due to its thin layer of abstraction and low overhead, C allows efficient implementations of algorithms and data structures, which is useful for programs that perform a lot of computations. For example, the GNU Multi-Precision Library, the GNU Scientific Library, Mathematica and MATLAB are completely or partially written in C.
C is sometimes used as an intermediate language by implementations of other languages, sometimes referred to as C intermediate language (CIL). This approach may be used for portability or convenience; by using C as an intermediate language, it is not necessary to develop machine-specific code generators. C has some features, such as line-number preprocessor directives and optional superfluous commas at the end of initializer lists, which support compilation of generated code. However, some of C's shortcomings have prompted the development of other C-based languages specifically designed for use as intermediate languages, such as C--. Several other tools use CIL as a way to have access to a C abstract syntax tree. Some of these utilities are Frama-C (a framework for analysis of C programs) or Compcert (a C compiler proven in Coq). CIL was originally designed and implemented in 2002 by George Necula et al.
C has also been widely used to implement end-user applications, but much of that development has shifted to newer languages.

Related languages
C has directly or indirectly influenced many later languages such as C#, D, Go, Java, JavaScript, Limbo, LPC, Perl, PHP, Python, and Unix's C Shell. The most pervasive influence has been syntactical: all of the languages mentioned combine the statement and (more or less recognizably) expression syntax of C with type systems, data models and/or large-scale program structures that differ from those of C, sometimes radically.
Several C or near-C interpreters exist, including Ch and CINT, which can also be used for scripting.
When object-oriented languages became popular, C++ and Objective-C were two different extensions of C that provided object-oriented capabilities. Both languages were originally implemented as source-to-source compilers; source code was translated into C, and then compiled with a C compiler.
The C++ programming language was devised by Bjarne Stroustrup as an approach to providing object-oriented functionality with a C-like syntax. C++ adds greater typing strength, scoping and other tools useful in object-oriented programming, and permits generic programming via templates. Nearly a superset of C, C++ now supports most of C, with a few exceptions.
Objective-C was originally a very "thin" layer on top of C, and remains a strict superset of C that permits object-oriented programming using a hybrid dynamic/static typing paradigm. Objective-C derives its syntax from both C and Smalltalk: syntax that involves preprocessing, expressions, function declarations, and function calls is inherited from C, while the syntax for object-oriented features was originally taken from Smalltalk.
In addition to C++ and Objective-C, Ch, Cilk and Unified Parallel C are nearly supersets of C.

Reference

I followed the following references to complete my project report:

Internet

Interview

Books

Magazines

Newspapers
Conclusion
C is a great programming language that can make programming a lot of fun. One of the best ways to learn is by taking a programming class. See if you can take a class at your school, or take a class at night school. Programming in C is a skill that could end up saving you your job or help you get a better job.