Simple Calculator - printing the result

cmong (2)
Hello, i'm making a simple calculator and have done it all right where you can input everything, all the functions are there, but when i run the program it will come to displaying the result and it will always equal zero, any help on this would be appreciated, i just need it to say 8+8 = 16 rather than 8+8 = 0, i don't know whether its just displaying the results as 0, or not displaying it at all, the code will follow below, thank you!

Also any tips on how i could possibly make the calculator better would be helpful, although its for my assignment so i have to use functions!

code:

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#include<iostream>

using namespace std;

double num3;
double num2;

double result;
char operation;
char a;
int repeat;

double addition()
{
result = num3 + num2;
return (result);
}

double subtraction()
{
result = num3 - num2;
return (result);
}

double division()
{	
result = num3 / num2;
return (result);
}

double multiplication()
{
result = num3 * num2;
return (result);
}

int main()
{



cout << "Please enter a number: ";
cin >> num3;

cout << "Please enter another number: ";
cin >> num2;

cout << "\n\n\n";

cout << "Select the desired function:\n";
cout << "+ Addition\n";
cout << "- Subtraction\n";
cout << "* Multiplication\n";
cout << "/ Division\n";
cout << "Selection: ";
cin >> operation;


cout << "\n\n\n";

switch(operation)
{
case '+':
cout << "The sum of " << num3 << "and "<< num2 << "equals" << addition << endl;
break;
case '-':
cout << "The difference of " << num3 << " and " << num2 << " is " << subtraction << endl;
break;
case '*':
cout << "The product of " << num3 << " and " << num2 << " is " << multiplication << endl;
break;
case '/':
cout << "The quotient of " << num3 << " and " << num2 << " is " << division << endl;
break;

default:
cout << "Invalid selection\n";



}
system ("pause");
return 0;
}
MikeyBoy (5631)
You need to go back to your textbook and re-read how to call a function. Nowhere in your code are you actually calling the functions addition, subtraction etc.

I'm very surprised it's showing 0 as the result, though.
ajh32 (659)
The reason you result is zero is because you're not calling your functions. I also suggest that you avoid declaring your variables with global scope, but instead keep them local.

I have revised your code, and added

(1) a do ... while loop so that your program will keep running until the user tells it to quit
(2) added a function which will check that the user has entered a valid number

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#include<iostream>
#include <conio.h>

using namespace std;


int get_number(char* prompt)
{
   cout << "\n" << prompt;
   int number(0);
   cin >> number;

   while(!cin.good())
   {
      cin.clear();
      cin.ignore(numeric_limits<streamsize>::max(), '\n');
      cout << "\nYou didn't enter a number. " << prompt;
      cin >> number;
   }

   cin.clear();
   cin.ignore(numeric_limits<streamsize>::max(), '\n');
   return number;
}

double addition(int num1, int num2)
{
   return num1 + num2;
}

double subtraction(int num1, int num2)
{
   return num1 - num2;
}

double division(int num1, int num2)
{	
   return num1 / num2;
}

double multiplication(int num1, int num2)
{
   return num1 * num2;
}

int main()
{
   bool running(true);

   do
   {
      char operation;

      cout << "\n\n\n";

      cout << "Select the desired function:\n";
      cout << "+ Addition\n";
      cout << "- Subtraction\n";
      cout << "* Multiplication\n";
      cout << "/ Division\n";
      cout << "q Quit\n";
      cout << "Selection: ";
      cin >> operation;
      cout << "\n\n\n";

      running = operation != 'q' && operation != 'Q' ? true : false;

      if (running)
      {
         int num1 = get_number("Please enter a number: ");
         int num2 = get_number("Please enter another number: ");

         cout << endl;

         switch(operation)
         {
            case '+':
               cout << "The sum of " << num1 << "and " << num2 << " equals " << addition(num1, num2) << endl;
               break;
            case '-':
               cout << "The difference of " << num1 << " and " << num2 << " is " << subtraction(num1, num2) << endl;
               break;
            case '*':
               cout << "The product of " << num1 << " and " << num2 << " is " << multiplication(num1, num2) << endl;
               break;
            case '/':
               cout << "The quotient of " << num1 << " and " << num2 << " is " << division(num1, num2) << endl;
               break;
            default:
               cout << "Invalid selection\n";
         }
      }
   } while (running);

   cout << "pause";
   getch();

   return 0;
}
ajh32 (659)
Also, rather than having specific function to deal with your arithmetic operations, you could write a class to encapsulate these operations on your class instance. This is then more natural and is how you were trying to code the solution:

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#include<iostream>
#include <conio.h>

using namespace std;


int get_number(char* prompt)
{
   cout << "\n" << prompt;
   int number(0);
   cin >> number;

   while(!cin.good())
   {
      cin.clear();
      cin.ignore(numeric_limits<streamsize>::max(), '\n');
      cout << "\nYou didn't enter a number. " << prompt;
      cin >> number;
   }

   cin.clear();
   cin.ignore(numeric_limits<streamsize>::max(), '\n');
   return number;
}


class Calculator
{
public:
   Calculator(int num)
      : number(num)
   {
   }

   friend std::ostream& operator << (std::ostream& os, const Calculator& c)
   {
      os << c.number;
      return os;
   }

   friend Calculator operator + (Calculator lhs, const Calculator& rhs)
   {
      lhs += rhs;
      return lhs;
   }

   friend Calculator operator - (Calculator lhs, const Calculator& rhs)
   {
      lhs -= rhs;
      return lhs;
   }

   friend Calculator operator * (Calculator lhs, const Calculator& rhs)
   {
      lhs *= rhs;
      return lhs;
   }

   friend Calculator operator / (Calculator lhs, const Calculator& rhs)
   {
      lhs /= rhs;
      return lhs;
   }

   Calculator& operator += (const Calculator& rhs)
   {
      number += rhs.number;
      return *this;
   }

   Calculator& operator -= (const Calculator& rhs)
   {
      number -= rhs.number;
      return *this;
   }

   Calculator& operator *= (const Calculator& rhs)
   {
      number *= rhs.number;
      return *this;
   }

   Calculator& operator /= (const Calculator& rhs)
   {
      number /= rhs.number;
      return *this;
   }
	
private:
   int number;
};

int main()
{
   bool running(true);

   do
   {
      char operation;

      cout << "\n\n\n";

      cout << "Select the desired function:\n";
      cout << "+ Addition\n";
      cout << "- Subtraction\n";
      cout << "* Multiplication\n";
      cout << "/ Division\n";
      cout << "q Quit\n";
      cout << "Selection: ";
      cin >> operation;
      cout << "\n\n\n";

      running = operation != 'q' && operation != 'Q' ? true : false;

      if (running)
      {
         int num1 = get_number("Please enter a number: ");
         int num2 = get_number("Please enter another number: ");

         Calculator c1(num1), c2(num2);

         cout << endl;

         switch(operation)
         {
            case '+':
               cout << "The sum of " << num1 << " and " << num2 << " equals " << c1 + c2 << endl;
               break;
            case '-':
               cout << "The difference of " << num1 << " and " << num2 << " is " << c1 - c2 << endl;
               break;
            case '*':
               cout << "The product of " << num1 << " and " << num2 << " is " << c1 * c2 << endl;
               break;
            case '/':
               cout << "The quotient of " << num1 << " and " << num2 << " is " << c1 / c2 << endl;
               break;
            default:
               cout << "Invalid selection\n";
         }
      }
   } while (running);

   cout << "pause";
   getch();

   return 0;
}
Last edited on
cmong (2)
thank you guys! didn't expect help so quickly! ajh32: although your code looks complicated i can make sense and it really helps so thanks! although wee haven't learnt classes in our lectures yet so i'm unable to do that.
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