Console calculator

Question

I am a newbie programmer learning some C++. One of the exercises in my book asked me to write a basic console calculator that takes 2 numbers and an operation as input. I have done so and the program compiles (both with clang++ and g++) and runs fine.

I would like to know if:

• I am making mistakes in my code that the compiler is allowing me to get away with
• If my code can be made more resource efficient and/or shorter in length

#include <iostream>
using namespace std;
int main()
{
char operation;
double first_number;
double second_number;
double solution = 0;

cout << "This is a basic calculator program, enter the first number.\n";
cout << "First number:";
cin >> first_number;

cout << "Enter second number:";
cin >> second_number;

cout << "\nEnter an operation to perform, choose one from this list: +,-,/,*\n";
cout << "Enter your operation:";
cin >> operation;
cin.ignore();

if (operation != '+' && operation != '-'&& operation != '/'&& operation != '*')
    {
        cout << "\nInvalid operation! Aborting!";
        cout << "\nPress Enter to exit.";
        cin.get();
        return 1;
    }//end if

if (operation == '+')
    {
        solution = first_number + second_number;
        cout << "\nYour answer is: " << solution << "\nPress Enter to exit.\n";
        cin.get();
        return 0;
    }//end if

if (operation == '-')
    {
        solution = first_number - second_number;
        cout << "\nYour answer is: " << solution << "\nPress Enter to exit.\n";
        cin.get();
        return 0;
    }//end if

if (operation == '*')
    {
        solution = first_number * second_number;
        cout << "\nYour answer is: " << solution << "\nPress Enter to exit.\n";
        cin.get();
        return 0;
    }//end if

if (operation == '/')
    {
        if ( second_number == 0 )
        {
            cout << "\nYou can't divide by zero! Aborting!";
            cout << "\nPress Enter to exit.";
            cin.get();
            return 2;
        }//end if
        solution = first_number / second_number;
        cout << "\nYour answer is: " << solution << "\nPress Enter to exit.\n";
        cin.get();
        return 0;
    }//end if


return 0;
}//end main

Answer 1

I'd try something like this. This is more robust as it checks for a 0 as the denominator and an invalid operation character.

Checking the former before attempting a calculation would be best, though you can still have it ask again for a proper denominator instead of just terminating the program right away. I did the latter here anyway for simplicity.

Checking the latter would involve either terminating the program right away or by throwing an exception since calculate() must return something (throw would replace return here, but should only be used in case of an error).

#include <cstdlib>   // EXIT_FAILURE
#include <iostream>
#include <stdexcept> // std::logic_error

float calculate(const char operation, const float left, const float right)
{
    switch (operation)
    {
        case '+': return left + right;
        case '-': return left - right;
        case '*': return left * right;
        case '/': return left / right;
        default: throw std::logic_error("unsupported operator");
    }
}

int main()
{
    std::cout << "Enter your two numbers: \n\n";
    float left, right;
    std::cin >> left >> right;

    std::cout << "\nEnter your operation (+, -, *, /): ";
    char operation;
    std::cin >> operation;

    // terminate right away if dividing by zero
    if (operation == '/' && right == 0)
    {
        std::cerr << "Cannot divide by 0";
        return EXIT_FAILURE;
    }

    float result;

    // attempt the calculation (will throw if failed)
    try
    {
        result = calculate(operation, left, right);
    }
    // if it fails - catch exception, display it, then terminate
    catch (std::logic_error const& e)
    {
        std::cerr << "Error: " << e.what();
        return EXIT_FAILURE;
    }

    std::cout << "\nResult = " << result;
}

Answer 2

You are duplicating a lot of code. You might want to put

cout << "\nYour answer is: " << solution << "\nPress Enter to exit.\n";
    cin.get();
    return 0;

after all if conditions, so you will save a lot of space, since these three lines are repeated for each 'if'. In that case, however, you might want to replace your "if"s with "else if". You can also output more than 1 line at a time like this:

cout << "some text" << "some more text" << "and some more";

To end the line, you can also use 'endl' instead of "\n":

cout << "some text" << endl;

So your code can look like this:

 #include <iostream>
 using namespace std;
 int main()
 {
 //it is always a good idea to initialize variables right away. 
 char operation = 0;
 double first_number = 0;
 double second_number = 0;
 double solution = 0;

 cout << "This is a basic calculator program, enter the first number." << endl;
 cout << "First number:";
 cin >> first_number;

 cout << endl << "Enter second number:";
 cin >> second_number;

 cout << endl << "Enter an operation to perform, choose one from this list: +,-,/,*\n";
 cout << "Enter your operation:";
 cin >> operation;
 cin.ignore();

 if (operation != '+' && operation != '-'&& operation != '/' && operation != '*')
 {
    cout << endl << "Invalid operation! Aborting!" << endl << "Press Enter to exit.";
    cin.get();
    return 1;
 }//end if

 if (operation == '+')
    solution = first_number + second_number;

 else if (operation == '-')
    solution = first_number - second_number;

 else if (operation == '*')
    solution = first_number * second_number;

 else if (operation == '/')
 {
    if ( second_number == 0 )
    {
        cout << endl << "You can't divide by zero! Aborting!";
        cout << endl << "Press Enter to exit.";
        cin.get();
        return 2;
    }//end if
    solution = first_number / second_number;
 }//end if

 ///Output starts here
 cout << endl << "Your answer is: " << solution << endl << "Press Enter to exit." << endl;
 cin.get();
 return 0;
 }//end main

Answer 3

You might want to check that your two numbers coming in are in fact numbers, if someone were to enter a letter, your program will crash. You might also want to split the operations up into other functions, it makes code more readable/ debug-able. Lastly, when using cout and cin, don't create new lines using the backslash n character \n, use << endl; which simply ends the line.