#include <iostream>
#include <string>
 
using namespace std;
 
void menu(int a, int b, int c, int d, char symbol);
 
void addFractions(int a,int b, int c, int d, int &numerator, int &denominator);
 
void subtractFractions(int a, int b, int c, int d, int &numerator, int &denominator);
 
void multiplyFractions (int a, int b, int c, int d, int &numerator, int &denominator);
 
void divideFractions (int a, int b, int c, int d, int &numerator, int &denominator);
 
//-------------------------------------------------------------------------
int main()
{
  int a, b, c, d;
  int numerator;
  int denominator;
  char symbol;
  cout << "first, we will need your numerators/denominators." << endl;
  cout << "What is your first fractions numerator?" << endl;
  cin>> a;
  cout << "What is your first fractions denominator?" << endl;
  cin >> b;
  cout << "What is your second fractions numerator?" << endl;
  cin >> c;
  cout << "What is your second fractions denominator?" << endl;
  cin >> d;
  while (d == 0 || b == 0)
  {
    if (d == 0)
    {
      cout << "Your second fraction has a 0 in the denominator, what would" <<
              " you like to change it to?" << endl;
      cin >> d;
    }
    if (b == 0)
    {
      cout << "Your first fraction has a 0 in the denominator, what would" <<
              " you like to change it to?" << endl;
      cin >> b;
    }
  }
  menu(a, b, c, d, symbol);
  return 0;
}
 
//--------------------------------------------------------------------
 
void menu(int a, int b, int c, int d, char symbol)
{
  int numerator, denominator;
  cout << "Have fractions that need solving??" << endl;
  cout << "Well, luckily for you, you chanced upon a fractions calculator"
  << endl;
  cout << "First, we will need the operation you wish to perform." <<
  endl;
  cout << "choose one of the following: + (addition), - " <<
  "(subtraction), * (multiplication), and finally / (division)." << endl;
  cin >> symbol;
  cout << endl;
 
  switch (symbol)
  {
  case '*':
    multiplyFractions(a,b,c,d,numerator, denominator);
    cout << "Answer is " << numerator << "/" << denominator << endl;
    system("pause>nul");
    break;
  case '/':
    divideFractions(a,b,c,d,numerator, denominator);
    cout << "Answer is " << numerator << "/" << denominator << endl;
    system("pause>nul");
    break;
  case '+':
    addFractions(a, b, c, d, numerator, denominator);
    cout << "Answer is " << numerator << "/" << denominator << endl;
    system("pause>nul");
    break;
  case '-':
    subtractFractions(a,b,c,d,numerator, denominator);
    cout << "Answer is " << numerator << "/" << denominator << endl;
    system("pause>nul");
    break;
  default:
    cout << "Invalid input, pay better attention next time." << endl;
  }
}
 
void addFractions (int a, int b, int c, int d, int &numerator, int &denominator)
{
  numerator = (a*d) + (b*c);
  denominator = (b*d);
}
 
void subtractFractions (int a, int b, int c, int d, int &numerator, int &denominator)
{
  numerator = (a*d)-(b*c);
  denominator = (b*d);
}
 
void multiplyFractions(int a, int b, int c, int d, int &numerator, int&denominator)
{
  numerator = (a*c);
  denominator = (b*d);
}
 
void divideFractions(int a, int b, int c, int d, int &numerator, int &denominator)
{
  numerator = (a*d);
  denominator = (b*c);
}