Does ISO C give allocated memory a hang after program termination?

An interesting point arose with some of my colleagues, some of whom claim that you always need a freememory, that you are mallocunimportant. Although I always thought it was good practice overall, some others argued that it was not necessary in a program such as:

#include <stdio.h>
#include <stdlib.h>
int main (void) {
    char *mem = malloc (1000);
    if (mem != NULL) {
        // do something with mem
    }
    // memory not freed
    return 0;
}

Their statement was that the memory will be cleared when the process is complete.

Now, being the local standard uber-geek, they turned to me for clarification and, to my surprise, it seems that always a free crowd can really be right.

Turning to C11, 5.1.2.2.3 Program terminationhe simply claims that reaching the end is mainidentical to the challenge exit.

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7.22.3.

7.22.3 Memory management functions , malloc free. , , . :

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