Division Problem

[supness]

I am trying to make a simple math program, everything else works fine, the adding, subtracting, multiplication, but the division seems to crash quite a bit(I've marked the code where it crashes), and I'm not sure why that is. Any one care to help out? Thanks in advance, and I've also taken a look around the forums and FAQs but couldn't find an answer.

PS. I'm Using Dev-C++

#include <iostream>
using namespace std;

int y;
int a, b, c, d;
int r, w;
int dt;

int main()
{
    st:
    srand((unsigned)time(0));      
    system("cls");
    cout << "Welcome to Math Helper\n";
    cout << "Input ''-1'' at any time to quit\n";
    cout << "Input ''-2'' at any time to return to the main menu\n";
    system("PAUSE");
    
    mm:
       r = 0;
       w = 0;             
       system("cls");
       cout << "Main Menu:\n";
       cout << "What would you like help with?\n";
       cout << "1 = Addition\n" ;
       cout << "2 = Subtraction\n";
       cout << "3 = Multiplication\n";
       cout << "4 = Division\n";
       cin >> y;
   
   switch (y)
      {
          case -1:
             goto end;  
          case 1:
             goto add;
          case 2:
             goto sub;
          case 3:
             goto mul;
          case 4:
             goto div;
          default:
             cout << "Please choose a valid number\n";
             system("PAUSE");
             goto mm;
      }      
   
   
   add:
      
      gna:
         a = (rand()%100);
         b = (rand()%100);
         c = (a + b);
         
         system("cls");
         cout << "Answer Stats: <Right: " << r << "> Wrong: <" << w << ">\n";
         cout << "Answer: " << a << " + " << b << " = ?\n";
         cin >> d;   
         
         if ( d == -2)
            {
                goto mm;   
            }
         
         else if ( d == -1)
            {
                goto end;   
            }
         
         else if (d == c)
            {
              cout << "Correct \n";
              system("PAUSE");
              r = (r + 1);
              goto gna;
            }        
         else
            {
                cout << "Incorrect \n";
                system("PAUSE");
                w = (w + 1);
                goto gna;
            }     
   sub:
      gns:
         a = (rand()%50);
         b = (rand()%50);
         c = (a - b);
         
         if (a < b | c < 0)
            {
                goto gns;
            }
         
         
         system("cls");
         cout << "Answer Stats: <Right: " << r << "> Wrong: <" << w << ">\n";
         cout << "Answer: " << a << " - " << b << " = ?\n";
         cin >> d;   
         
         if ( d == -2)
            {
                goto mm;   
            }
         
         else if ( d == -1)
            {
                goto end;   
            }
         
         else if (d == c)
            {
              cout << "Correct \n";
              system("PAUSE");
              r = (r + 1);
              goto gns;
            }        
         else
            {
                cout << "Incorrect \n";
                system("PAUSE");
                w = (w + 1);
                goto gns;
            }     
   
   
   mul:
      gnm:
         a = (rand()%12);
         b = (rand()%12);
         c = (a * b);
         
         system("cls");
         cout << "Answer Stats: <Right: " << r << "> Wrong: <" << w << ">\n";
         cout << "Answer: " << a << " * " << b << " = ?\n";
         cin >> d;   
         
         if ( d == -2)
            {
                goto mm;   
            }
         
         else if ( d == -1)
            {
                goto end;   
            }
         
         else if (d == c)
            {
              cout << "Correct \n";
              system("PAUSE");
              r = (r + 1);
              goto gnm;
            }        
         else
            {
                cout << "Incorrect \n";
                system("PAUSE");
                w = (w + 1);
                goto gnm;
            }     
   
   div://It crashes right here!! 
      gnd:
         a = (rand()%12);
         b = (rand()%12);
         c = (a / b);
         
         //This code tried to keep the math simple with no remainder
         dt = a % b;
         
         /*if (a < b | c < 0)
            {
                goto gnd;
            }
          */  
         if (dt != 0)
            {
                goto gnd;
            }
         
         
                 
         
         system("cls");
         cout << "Answer Stats: <Right: " << r << "> Wrong: <" << w << ">\n";
         cout << "Answer: " << a << " / " << b << " = ?\n";
         cin >> d;   
         
         if ( d == -2)
            {
                goto mm;   
            }
         
         else if ( d == -1)
            {
                goto end;   
            }
         
         else if (d == c)
            {
              cout << "Correct \n";
              system("PAUSE");
              r = (r + 1);
              goto gnd;
            }        
         else
            {
              cout << "Incorrect \n";
              system("PAUSE");
              w = (w + 1);
              goto gnd;
            }  
   
   end: 
      return 0;
}

[Faldrax]

My first comment would be AAAAARRRGGGHHHHHH goto's!!!!
Goto is generally regarded as a poor way to program, as it tends to lead to code that is difficult to maintain.
It is much better to use functions.

Back to your problem - well, 1 in 12 times b == 0, so you have a division by zero when calculating c. Add a test for b==0 before the division and either set b=1, or c=0 (depending on how you want to handle this case).

And get rid of the goto's... :-)

[Somelauw]

Fadrax:
Instead of testing if b == 0, why not making sure that b can't reach 0 in the first place?
b = 1 + rand%11

supness (OP):
I think the math for the division is too complicated. Why not multiply some random numbers first to make sure there never will be a remainder?

Also I would prefer functions and loops to get rid of the goto's like Faldrax already said, but that's your own choice. Most people will stop using these after a while automatically because it leads to spaghetti code.

Some joke:
When telling a programmer to: "go to heck", he is more offended by the "go to" than "heck"