When to free memory in C

main.c

#define _CRTDBG_MAP_ALLOC
#include <crtdbg.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>


int main(int argc, char* argv[]) {
    int* p = calloc(1, sizeof(int));
    int* q = p;
    *q = -1;
    free(p);
    _CrtDumpMemoryLeaks();
    return 0;
}