Question

I was making a simple calculator in C++. However the program does not completely function the way it should. When run, the trig if statement executes fine, however, the basic arithmetic else statement doesn’t work. I have determined that the code is not executing the else statement and was wondering how to fix it. The code inside the else statement works fine, as I have commented out the if statement. Help?

Here is my code:

#include "stdafx.h"
#include <iostream>
#include <string>
#include <cmath>


int main()
{
    double input = 0;
    double firstnumber = 0;
    double secondnumber = 0;


    std::string function;
    std::string operation;


    std::cout << "Enter your calculation: ";
    std::cin >> function;   


    if(function == "sin" || "cos" || "tan")
    {
        if(function == "sin")
        {
            std::cin >> input;
            std::cout << "The sine is " << sin(input) << std::endl;
            system("PAUSE");
        }
        else if(function == "cos")
        {
            std::cin >> input;
            std::cout << "The cosine is " << cos(input) << std::endl;
            system("PAUSE");

        }
        else if(function == "tan")
        {
            std::cin >> input;
            std::cout << "The tangent is " << tan(input) << std::endl;
            system("PAUSE");
        }
    }
    else
    {       

        firstnumber = ::atof(function.c_str());
        std::cin >> operation;
        std::cin >> secondnumber;


        double valueadd = firstnumber + secondnumber;
        double valuesubtract = firstnumber - secondnumber;
        double valuemultiply = firstnumber * secondnumber;
        double valuedivide = firstnumber / secondnumber;


        if(operation == "+")
        {      
            std::cout << " = " << valueadd << std::endl;
            system("PAUSE");
        }
        else if(operation == "-")
        {          
            std::cout << " = " << valuesubtract << std::endl;
            system("PAUSE");
        }
        else if(function == "*")
        {
            std::cout << " = " << valuemultiply << std::endl;
            system("PAUSE");
        }
        else if(function == "/")
        {
            std::cout << " = " << valuedivide << std::endl;
            system("PAUSE");
        }

        else
        {
            std::cout << "Error" << std::endl;
            return 0;
        }
    }
    return 0;
}

Answer 1

This line is wrong.

if(function == "sin" || "cos" || "tan")

It should be

if((function == "sin") || (function == "cos") || (function == "tan"))

Note that the check is actually meaningless because you already check for them each individually. You could tidy this up by doing this in a if, else if, else chain.