C

Appeared in:
1972
Influenced by:
Influenced:
Paradigm:
Typing discipline:
File extensions:
.c .h
Dialects:
Versions and implementations (Collapse all | Expand all):
Programming language

C is an imperative (procedural) general-purpose computer programming language developed in 1972 by Dennis Ritchie at the Bell Telephone Laboratories for use with the Unix operating system.

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 language.

Despite its low-level capabilities, the language was designed to encourage machine-independent programming. A standards-compliant and portably written C program can be compiled for a very wide variety of computer platforms and operating systems with little or no change to its source code. The language has become available on a very wide range of platforms, from embedded microcontrollers to supercomputers.

Elements of syntax:

Inline comments // (C99 only)
Nestable comments #if 0 ... #endif
Non-nestable comments /* ... */
Case-sensitivity yes
Variable identifier regexp [_a-zA-Z][_a-zA-Z0-9]*
Variable assignment =
Variable declaration type variable
Variable declaration with assignment type variable = value
Block { ... }
Physical (shallow) equality ==
Physical (shallow) inequality !=
Comparison < > <= >=, strcmp for strings
Function definition returntype f(type1 p1, type2 p2, ...)
Function call f(a, b, ...)
Function call with no parameters f()
If - then if (condition) ...
If - then - else if (condition) ... else ... OR ( condition ? ... : ... )
Loop forever while (1) ...
While condition do while (condition) ...
Do until condition do ...while (!condition)
For each value in a numeric range, 1 increment for (int i = 1; i <= 10; i++) ...
For each value in a numeric range, 1 decrement for (int i = 10; i >= 1; i--) ...

Examples:

Hello, World!:

Example for versions Turbo C++ 1.01, g++ 3.4.5, gcc 3.4.5, gcc 3.4.5 (Objective-C), gcc 4.2.4 
#include <stdio.h>

int main()
{
    printf("Hello, World!\n");
    return 0;
}

Factorial:

Example for versions gcc 3.4.5, gcc 3.4.5 (Objective-C), gcc 4.2.4

This example uses recursive factorial definition. Note that 13! and larger causes an overflow, so the last lines of the output look like this:

13! = 1932053504
14! = 1278945280
15! = 2004310016
16! = 2004189184

#include <stdlib.h> /* needed for EXIT_SUCCESS */
#include <stdio.h>

unsigned long long factorial(unsigned long long n)
{
    if (n == 0) {
        return 1;
    } else {
        return n * factorial (n - 1);
    }
}

int main(void)
{
    int n;
    for (n = 0; n <= 16; n++) {
        printf("%i! = %lld\n", n, factorial(n));
    }
    return EXIT_SUCCESS;
}

Fibonacci numbers:

Example for versions gcc 3.4.5, gcc 3.4.5 (Objective-C)

This example uses recursive definition of Fibonacci numbers. Note the difference from C++ example: loop counter must be declared outside of the loop, and printf is used for output instead of std::out. 

#include <stdio.h>

int fibonacci(int n)
{
    return ( n<=2 ? 1 : fibonacci(n-1) + fibonacci(n-2) );
}

int main(void)
{
    int n;
    for (n=1; n<=16; n++)
        printf("%d, ", fibonacci(n));
    printf("...\n");
    return 0;
}