Evaluates its first operand, and, if the resulting value is not equal to zero, evaluates its second operand. Otherwise, it evaluates its third operand, as shown in the following example:

a = b ? c : d;

is equivalent to:

if (b)
    a = c;
else 
    a = d;

This pseudo-code represents it : condition ? value_if_true : value_if_false. Each value can be the result of an evaluated expression.

int x = 5;
int y = 42;
printf("%i, %i\\n", 1 ? x : y, 0 ? x : y); /* Outputs "5, 42" */

The conditional operator can be nested. For example, the following code determines the bigger of three numbers:

big= a > b ? (a > c ? a : c)
           : (b > c ? b : c);

The following example writes even integers to one file and odd integers to another file:

#include<stdio.h>

int main()
{
    FILE *even, *odds;
    int n = 10;
    size_t k = 0;

    even = fopen("even.txt", "w");
    odds = fopen("odds.txt", "w");

    for(k = 1; k < n + 1; k++)
    {
        k%2==0 ? fprintf(even, "\\t%5d\\n", k)
               : fprintf(odds, "\\t%5d\\n", k);
    }
    fclose(even);
    fclose(odds);

    return 0;
}

The conditional operator associates from right to left. Consider the following:

exp1 ? exp2 : exp3 ? exp4 : exp5

As the association is from right to left, the above expression is evaluated as

exp1 ? exp2 : ( exp3 ? exp4 : exp5 )