cin causes runtime error - c++

Question

Here's the problem https://www.hackerrank.com/challenges/extra-long-factorials
Here's my code
#include <iostream>
using namespace std;
int main(){
int n;
cin >> n;
int product[200];
for (int i = 0; i < 200; i++)product[i] = 0;
product[0] = 1;
for (int i = 1; i <= n; i++){
int a[200], res[200];
for (int j = 0; j < 200; j++)a[j] = 0, res[j] = 0;
int n = i;
int k = 0;
while(n != 0){
a[k] = n % 10;
n = n / 10;
k++;
}
int at[200][200];
for (int p = 0; p < 200; p++){
for (int h = 0; h < 200; h++){
at[p][h] = 0;
}
}
int carry = 0;
for (int x = 0; x < 200; x++){
for (int d = 0; d < 200; d++){
at[x][x+d] = ((product[d] * a[x]) % 10) + carry;
carry = (product[x] * a[d]) / 10;
}
}
int carry2, temp;
for (int u = 0; u < 200; u++){
temp = 0;
for (int e = 0; e < 200; e++){
temp += at[e][u];
}
temp = (temp + carry2);
carry2 = temp/10;
res[u] = temp %10;
product[u] = res[u];
}
}
int f = 0;
for (; f < 200; f++){
if(product[200-f-1] != 0)break;
}
for (; f < 200; f++){
cout << product[200-f-1];
}
return 0;
}
It runs fine on gcc on my mac and gives a correct answer. However it gives a runtime error on the online judge as well as ideone.
I've debugged the code and the error is caused by cin >> n; It runs fine without it and gives a correct answer (which is 1). The test input that caused the error is 25 so it's not a big number. I dont know exactly what's the problem or how is it causing the error. Thank you.

Answer 1

This is the problem:
at[x][x+d] = ...
because both x and d run from 0 to 200, but at is an array on the stack, with size: [200][200] so obviously x+d will overwrite the code coming after the array declaration.
This is a classical buffer overflow :)
(Obviously, initializing carry2 won't hurt either, but not doing that will not give the core dump at 0x0, just some unexpected behaviour)