Ambiguous behavior of while() loop in c

Question

Since while loop terminates its execution for false expression, despite following are giving different outputs. Unable to trace

#include <stdio.h>
int main()
{
    //code snippet 1
    while(0){
        ;
    }
    printf("C");
    return 0;
}

this gives output

and

#include <stdio.h>
    int main()
    {
        //code snippet 2
        while(printf("%d")){
            ;
        }
        printf("c");
        return 0;
    }

this gives output

0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

Since printf() function returns the number of characters printed, and no character is being printed, therefore it should not result in an infinite loop as 0 has the logical value false.

It's not returning `0`. Try running `printf("%d", printf("%d"));` — sshashank124, Jan 13 '20 at 05:16
You can refer to the behaviour of printf without variable name https://stackoverflow.com/questions/437816/behaviour-of-printf-when-printing-a-d-without-supplying-variable-name — Rishikesh Raje, Jan 13 '20 at 05:23
is the output compiler dependent. I am using minGW on windows — SuspectBloom993, Jan 13 '20 at 05:24
thanks, RishikeshRaje sshashank124, actually it is using some garbage value — SuspectBloom993, Jan 13 '20 at 05:27
What do you mean, no character is being printed? It's obviously printing the character `0` over and over! Which call do you think is printing `0`? It's not the second one, that prints `c`. — user253751, Jan 13 '20 at 11:19

score 1 · Answer 1 · answered Jan 13 '20 at 06:06

1

The return value of your printf("%d") is not 0 (actually is a undefined behaviour).
See Printf with no arguments explanation

answered Jan 13 '20 at 06:06

Catalin Dumitrescu

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Ambiguous behavior of while() loop in c

1 Answers1