explanation for C program (uses comma operator)

Question

#include<stdio.h>
int main(){
    int i=0;
    while(i<4,5){
        printf("loop");
        i++;
    }
}

This code goes infinite loop. can anyone explain logic behind these?

Answer 1

In the code

 while(i<4,5)

is same as

 while(5)

which is always true.

As per the comma operator properties, quoting from C11, chapter 6.5.17/P2

The left operand of a comma operator is evaluated as a void expression; there is a sequence point between its evaluation and that of the right operand. Then the right operand is evaluated; the result has its type and value

Point to note: With this code, you'll hit undefined behaviour due to signed overflow in i++.