comma separated expression in while loop in C

Question

I never saw such a while statement before.

while(printf(\"> \"), fgets(str, 100, stdin), !feof(stdin)) {
..
..
}

I read

Answer 1

The comma operator is best thought of as, well, an operator. Just like + is an operator, so that 2 + 3 is an expression (which happens to result in a value of 5), so too , is an operator, and thus 0, 1 is a valid expression (which happens to result in a value of 1, since that was the last operand).