Why it results all the time same whether I allocated only for 40 members?

Question

#include <stdio.h>
#include <stdlib.h>
int main() {
int *ptr;
ptr = malloc(10*sizeof(*ptr)); /* a block of 10 ints */
if (ptr != NULL) {
*(ptr+210) = 50;
}
printf("%d", *(ptr + 210));
return 0;
}

Answer 1

You assign 50 at pointer offset 210 in a memory area outside array bounds, sometimes you dont crash, but you can corrupt memory.

It is similar to a dangling pointer, it point to memory that it does not own (or no longer owns).
For errors like this, a crash is best thing that can happen to alert you that something is wrong. but it does not happen always.