if statement

Conditionally executes code.

Used where code needs to be executed only if some condition is true.

Syntax

Explanation

expression must be an expression of any scalar type.

If expression compares not equal to the integer zero, statement_true is executed.

In the form (2), if expression compares equal to the integer zero, statement_false is executed.

enum {a, b};
int different(void)
{
    if (sizeof(enum {b, a}) != sizeof(int))
        return a; // a == 1
    return b; // b == 0 in C89, b == 1 in C99
}

Notes

The else is always associated with the closest preceding if (in other words, if statement_true is also an if statement, then that inner if statement must contain an else part as well):

int j = 1;
if (i > 1)
   if(j > 2)
       printf("%d > 1 and %d > 2\n", i, j);
    else // this else is part of if(j>2), not part of if(i>1) 
       printf("%d > 1 and %d <= 2\n", i, j);

If statement_true is entered through a goto, statement_false is not executed.

Keywords

if, else

Example

#include <stdio.h>
 
int main(void)
{
    int i = 2;
    if (i > 2) {
        printf("first is true\n");
    } else {
        printf("first is false\n");
    }
 
    i = 3;
    if (i == 3) printf("i == 3\n");
 
    if (i != 3) printf("i != 3 is true\n");
    else        printf("i != 3 is false\n");
}

first is false
i == 3
i != 3 is false

References