Understanding malloc: Why doesn't my program crash, when I exceed allocated memory?

I have tinkered around with malloc to understand better how is works.
I wrote this program:

int *array = (int *)malloc(100 * sizeof(int));

for (int i = 0; i < 5000; i++) {
    array[i] = 10;
}
// Element with index 4999 has a correct value 
printf("%d\n", array[4999]);

return 0;

Actually I would expect the program to crash, because I have allocated memory for only 100 integer. But I write 5000 integers into the pointer-array. The element 5000 in the array has even the correct value.

What happens here?

Does it automatically allocate more memory, when needed? But in this case: What sense does the initial allocation have, which is given as an argument?

>Solution :

You are using memory which does not belong to you. Various things could happen, including a crash but also you might read a different value than you write, or you might cause your fax-modem to dial the White House when you write.

It’s like building a house on land you don’t own. Maybe you can live there undisturbed for years. Maybe the government will tear it down. Maybe the land is a disused uranium mine.