Runtime error in Ideone but works fine in codeblocks - c++

Question

I tested this code on codeblocks and it is working fine but when i run this on Ideone i get runtime error and SIGSEGV error on OJ. I read online that SIGSEGV error is caused due to restricted memory access. But if it is doing so why isn't codeblocks complaining......
#include <bits/stdc++.h>
using namespace std;
int main()
{
ios_base::sync_with_stdio(false);
int t, i, j, k, x, temp;
int num1[10000], num2[10000];
char c;
bool f = true;
cin >> t;
while (t--)
{
for (i = 0; i < 10000; i++)
{
num1[i] = 0;
num2[i] = 0;
}
i = 0;
j = 0;
while (!isspace(c = getchar()))
num1[i++] = c - '0';
while (!isspace(c = getchar()))
num2[j++] = c - '0';
x = i > j ? i : j;
temp = 0;
for (k = 0; k < x; k++)
{
i = temp + num1[k] + num2[k];
if (f)
{
if (i % 10 != 0)
{
f = false;
cout << i % 10;
}
}
else cout << i % 10;
temp = i / 10;
}
if (temp != 0)
cout << temp;
cout << endl;
f = true;
}
return 0;
}

Answer 1

This:
while (!isspace(c = getchar()))
will keep going until it finds a space character. If there's no space after the final input value, then getchar() will return EOF, which you'll truncate to char and pass to isspace, giving undefined behaviour. The chances are that isspace will return false, and you'll loop forever, off the end of your fixed size array, until you reach unaddressable memory and cause a segmentation fault.
Always check input before using it. You'll also have big problems if there's no input, since you don't check whether t was successfully read.