Keywords are reserved words defined by the C language. They have predefined meanings and cannot be used as identifiers such as variable or function names.

#include <stdio.h>

int main()
{
    int number = 10;

    if (number > 0)
    {
        printf("Positive\n");
    }

    return 0;
}

Example Output #

Positive

Explanation #

The program uses several C keywords:

int
if
return

Each has a specific language-defined meaning.

For example:

int number = 10;

uses int to specify the type of number.

if (number > 0)

uses if to conditionally execute a statement.

return 0;

uses return to terminate the main() function and provide its return value.

C Keywords #

The following table lists the keywords defined by the C language through C23:

The exact keyword set depends on the C standard being used. Older standards such as C90, C99, C11, and C17 contain fewer keywords than C23.

Keywords cannot be declared as ordinary identifiers:

int return = 10;   /* Invalid */

A name such as return_value is valid because it is an identifier, not the keyword return.