A simple addition,substraction,multiplication and division program

A simple C++ calculator program to calculate addition, subtraction, multiplication and addition...

#include <iostream>
#include <string>
using namespace std;

int main()
{
    //input declarations as doubles for total and counter
    double total = 0, counter =0;
    //input declarations sign and Q as character
    char sign, Q = 0;
    //input declaration value as double
    double value;



        //A do..while will loop forever (or until we hit the break statement)
        do 
        {
            //The current value is 0.
            cout << "Result :"<<" "<< total << '\n';

            //Please enter an operation
            cout << "Please enter an operation and number : ";
        cin >> sign;

        //If the operation is Q, the program will end.
        if (sign != 'Q')

        cin >> value;
            cin.ignore();


            // If the value input is <=0, you can't divide anything by zero. 
            if (value <= 0)
            {
                cout << "Unknown Operator " << sign <<'\n' ;
            }

            //Otherwise procede with the calulator program
            else
            {
                //If the operation is equal to '+', then the total is added.
                if (sign == '+')
                { 
                    total += value;
                }

                // If the operation is equal to '-', then the value is subtracted from the previous number input. 
               开发者_如何学JAVA else
                {
                    if (sign == '-')
                    {
                        total -= value;
                    }

                    // If the operation is equal to '*', then the value is multiplied to the previous number input. 
                    else
                    {
                        if (sign == '*')
                        {
                            total *= value;
                        }

                        // If the operation is equal to '/', then the value is divided by the previous number input.
                        else 
                        {
                            if ((sign == '/')&&(value != 0))
                            {
                                total /= value;
                            }
                        }
                    }
                }
            }
        }



            //While the operation is not equal to 'Q', the program will run.
            while (sign != 'Q');



        return 0;
}

The coding for the above program has no error but if i press "Q" to quit,it will display the last result non-stop. .Over and over and over and over again. . . Anyway,anyone know how to add square root to the program. .

Replace if (sign != 'Q') ... by if (sign == 'Q') break;

• This will fix numerous possible errors.
• This will make your code more readable by using less indentation and braces.

EDIT: as someone mentionned, you should probably be checking lowercase too. (if (sign == 'Q' || sign == 'q')).

As a simple exercise I have refactored your program to make it simpler. I don't promise it works, but it should give you a nice foundation to build on:

#include <iostream>
#include <string>
using namespace std;

int main()
{
  //input declarations as doubles for total and counter
  double total = 0, counter =0;
  //input declarations sign and Q as character
  char sign = 0;
  //input declaration value as double
  double value;

  //A do..while will loop forever (or until we hit the break statement)
  do 
  {
    //The current value is 0.
    cout << "Current result: " << total << '\n';

    //Please enter an operation
    cout << "Please enter an operation (or Q to quit) and number: ";
    cin >> sign;

    //If the operation is Q, the program will end.
    if (sign == 'Q' || sign == 'q') {
      cout << "See you!\n";
      break;
    }

    // If the input cannot be transformed into a double
    // abort loop and try again
    if (!(cin >> value)) {
      cerr << "Invalid value entered, try again\n";
      continue;
    }

    switch(sign)
    {
    case '+': total += value; break;
    case '-': total -= value; break;
    case '*': total *= value; break;
    case '/':
      if (value == 0) {
        cerr << "Divide by 0 prevented!\n";
      } else {
        total /= value; break;
      }
    default:
      cerr << "Unknown sign: " << sign << "\n";
    }

  } while (true);

  return 0;
}

The main points:

• avoid indentation when possible, they hamper readability (prefer continue/break)
• use a switch when possible (it's possible for char and numbers)
• check for errors when necessary: the conversion from the user input to the double could fail, 0 might be entered

#include <math.h>
double result = sqrt (value);

For square root, #include <math> double r=sqrt(e);

Concerning your other issue : please indent your code better ;-)

Are you sure you didn't forget to put a block after this line ? if (sign != 'Q')

Simplest way, use a debugger in step mode and you'll understand!