How does this recursive function work properly when it doesn't return a value?

Question

include <stdio.h>
int sum = 1;
int fact(int num){
    if (num == 0){
        return 1;
    }
    fact(num -1);
    sum *=num;
}

int main()
{
    int num = 5;  
    printf("%d ", fact(num));
    return 0;
}

The output of the above program prints 120 though I don't have a return from the recursive condition. I do have a basic understanding of how recursive calls creates a function on the stack. Could someone explain to me how this program prints output without any return?

Update: The below code return value of 1 as expected.

#include <stdio.h>
int sum = 1;
int fact(int num){
    if (num == 0){
        return 1;
    }
    num * fact(num -1);
}

int main()
{
    int num = 5;  
    printf("%d ", fact(num));
    return 0;
}