C Programming - Operators - Comma Operator

Comma Operator

The comma operator has left-to-right associativity. Two expressions separated by a comma are evaluated left to right. 
The left operand is always evaluated, and all side effects are completed before the right operand is evaluated.
The comma operator is mainly useful for obfuscation.
The comma operator allows grouping expression where one is expected.
Commas can be used as separators in some contexts, such as function argument lists.
Example :

#include <stdio.h>
int main ()
{
    int i = 10, b = 20, c= 30;

    // here, we are using comma as separator
    i = b, c;

    printf("%i\n", i);

    // bracket makes its one expression.
    // all expression in brackets will evaluate but
    // i will be assigned with right expression (left-to-right associativity)
    i = (b, c);
    printf("%i\n", i);

    return 0;
}

Output :
    20
    30