How to allow user input of numbers and operators?

Question

how would I add a function that allows the user to input something like 2 + 2 or 10 / 5 then simply run the objects to calculate this as they would when they enter it manually using my "Enter first input" statements. So as part of the assignment I need to allow the user to input something like 10 / 5 + 1 / 2 in the console. I also need to be able to allow for operator overloading and I'm not sure if my program is currently allowing this. Any help would be appreciated. Thanks!

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

using namespace std;

class Rational
{
    private:
        float numInput;

    public:
        Rational(): numInput(0)
        {}

        void getValues()
        {           
            cout << "Enter number: ";
            cin >> numInput;
        }

        void showValues()
        {
            cout << numInput << endl;
        }

        Rational operator + (Rational) const;
        Rational operator - (Rational) const;
        Rational operator * (Rational) const;
        Rational operator / (Rational) const;
};

Rational Rational::operator + (Rational arg2) const
{
    Rational temp;
    temp.numInput = numInput + arg2.numInput;
    return temp;
}

Rational Rational::operator - (Rational arg2) const
{
    Rational temp;
    temp.numInput = numInput - arg2.numInput;
    return temp;
}

Rational Rational::operator * (Rational arg2) const
{
    Rational temp;
    temp.numInput = numInput * arg2.numInput;
    return temp;
}

Rational Rational::operator / (Rational arg2) const
{
    Rational temp;
    temp.numInput = numInput / arg2.numInput;
    return temp;
}

int main()
{
    Rational mathOb1, mathOb2, outputOb;
    int choice;
    mathOb1.getValues();
    cout << "First number entered: ";
    mathOb1.showValues();
    cout << endl;
    cout << "Enter operator: + = 1, - = 2, * = 3, / = 4  ";
    cin >> choice;
    cout << endl;
    mathOb2.getValues();
    cout << "Second number entered: ";
    mathOb2.showValues();    cout << endl;

    switch (choice)
    {
        case 1:
            outputOb = mathOb1 + mathOb2;
            break;
        case 2:
            outputOb = mathOb1 - mathOb2;
            break;
        case 3:
            outputOb = mathOb1 * mathOb2;
            break;
        case 4:
            outputOb = mathOb1 / mathOb2;
            break;
        default:
            cout << "Invalid choice! " << endl;
    }
    cout << "Answer: ";
    outputOb.showValues();
    cout << endl;

    return 0;
}

score 0 · Accepted Answer · edited May 23 '17 at 12:28

You can't use cin >> {int}, that will just fail if you provide a char and you'll be stuck from there on.

Just use std::getline and parse out the tokens from there:

std::string expression;
std::getline(std::cin, expression);

You can then use any of the many, many ways to split a string into tokens as expressed in this question, and loop through the tokens and interpret them based on whether they are operators or numbers.

How to allow user input of numbers and operators?

1 Answers1