Cannot access memory at address 0x140018000

["learning c++" <learning_c@xxxxxxxxxxx>]

Hi,
I can run this program with my computer. But if I use GDB to run it step by 
step. there is always an error:
Cannot access memory at address 0x140018000

What is wrong with the code and the reason?

Thanks,


/* This program allows the user to enter to fraction and then.
  the program will print the fraction added together and reduced */


#include<iostream>
using namespace std;


void ReadFraction(int &Num, int &Denom, int &Num2, int &Denom2)
/* This function will allow the user to enter two fraction. */
{
       cout << "Enter the numerator for the first fraction: ";
       cin >> Num;
       cout << "Enter the denominator for the first fraction: ";
       cin >> Denom;
       cout << endl;
       cout << "Enter the numerator for the second fraction: ";
       cin >> Num2;
       cout << "Enter the denominator for the second fraction: ";
       cin >> Denom2;
       cout << endl;

}
void Reduce(int &Num, int &Denom, int &Num2, int &Denom2)
/* This function is called after ReadFraction(). This function will
  reduce the two fractions.
  Pre: Two Fractions
  Post: Two reduced fractions */
{
       int a, b, c, d, i, j = 0;

       a = Denom;
       b = Num;
       c = Denom2;
       d = Num2;


       for (i = a * b; i > 1; i--)
       {
               if ((a % i == 0) && (b % i == 0))
               {
                       a /= i;
                       b /= i;
               }
       }

       for (j = 50; j > 1; j--)
       {
               if ((c % j == 0) && (d % j == 0))
               {
                       c /= j;
                       d /= j;
               }
       }

       Denom = a;
       Num = b;
       Denom2 = c;
       Num2 = d;

}
void Reduce(int &Num, int &Denom)
/* This function is called from AddFraction(). The fraction added in
  AddFraction() is reduced here.
  Pre: One fraction added from two
  Post: A reduced fraction  */
{
       int a = 0;
       int b = 0;
       int i = 0;


       a = Denom;
       b = Num;


       for (i = 50; i > 1; i--)
       {
               if ((a % i == 0) && (b % i == 0))
               {
                       a /= i;
                       b /= i;
               }
       }


       Denom = a;
       Num = b;
}


//-------------------------------------------------------------------


void AddFraction(int &Num, int &Denom, int &Num2, int &Denom2)
/* This function is called after Reduce. This function adds the two
  fractions Reduce() reduced
  Pre: Two Fractions*/
{
       if (Denom != Denom2)
       {


               Num = Num * Denom2;
               Num2 = Num2 * Denom;
               Denom = Denom * Denom2;
               Denom2 = Denom2 * Denom;
               Num = Num + Num2;
       }
       else
       {
               Num = Num + Num2;
       }

       Reduce(Num, Denom);
}

void DisplayFraction(int &Num, int &Denom)
/* This function displays the reduced and added fraction. This
  function is called after AddFraction()
  Post: Prints fraction */
{
       cout << "The reduced and added fraction is " << Num << "/" << Denom 
<< endl;
}

int main()
{
       char an;

       do
       {
               int Num, Denom, Num2, Denom2 = 0;

               ReadFraction(Num, Denom,Num2,Denom2);
               Reduce(Num, Denom, Num2, Denom2);
               AddFraction(Num, Denom, Num2, Denom2);
               DisplayFraction(Num, Denom);
               cout << endl;

               cout <<"Would you like to do another fraction? ";
               cin >> an;
               cout << endl;
       } while ((an == 'y') || (an == 'Y'));


       return(0);
}

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