Making Calculator say "error" when dividing by 0

[DJLad16]

Right, first of all after about 12 years of doing maths. I've just learnt that if you get an error on any calculator if you try to divide by 0 i.e 7/0.
So after trying to divide by 0 on my calculator, it crashes (which I found a bit amusing) Therefore I tried to add a bit of code that will give an error when dividing by 0, but it always crashes when I try to divide by 0 after trying multiple things.
Please help.
Here's the code:

#include <iostream>
using namespace std;

int main()
{
      int a;
      int b;
      int sum;
      string userResponse;
      char userinput;

      do{

      cout << "\t / = Divide, * = Multiply";
      cout << "\n\nEnter a calculation: ";
      cin >> a;
      cin >> userinput;
      cin >> b;


    switch(userinput)
    {
        case '+' : sum = a + b;
        break;
        case '-' : sum = a - b;
        break;
        case '*' : sum = a * b;
        break;
        case '/' : sum = a / b;


    }

    cout << "\nThe total of those numbers are: " << sum << endl;


    if(sum > 20){
      cout << "\nHa, your number is greater than 20 \n";
      }
       if(sum < 20){
       cout << "\nCan't catch me out, your number is less than 20 \n";
       }
       if(sum == 20){
       cout << "\nYour number is equal to 20 \n";
       }

       cout << "\nDo you want to use is again (Yes/No) \n";
       cin >> userResponse;

       }while(userResponse == "Yes");
}

[codewalker]

It will always crash if you actually devise by zero (hardware interrupt). The trick would be to check if "b" is zero before you perform actual devision.