The comma operator , evaluates two or more expressions from left to right. The value of the entire comma expression is the value of the rightmost expression.

#include <stdio.h>

int main()
{
    int a;
    int b;

    a = (10, 20);

    b = (1, 2, 3, 4);

    printf("a = %d\n", a);
    printf("b = %d\n", b);

    return 0;
}

Example Output #

a = 20
b = 4

Explanation #

In:

a = (10, 20);

10 is evaluated first, followed by 20. The value of the entire expression is the value of the rightmost expression, so a receives 20.

Similarly:

b = (1, 2, 3, 4);

evaluates the expressions from left to right, and the complete expression produces 4.

The comma operator is different from commas used to separate function arguments or variable declarations. It specifically forms a single expression whose value is determined by its rightmost operand.