Fraction Calculator

//
//  Fraction.cpp
//  CS115-Assignment1
//
//  Created by Hayden Lueck on 2015-01-13.
//  Copyright (c) 2015 Hayden Lueck. All rights reserved.
//
//  Create a calculator that adds, subtracts, multiplies, and divides fractions
//

#include <iostream>
#include <string>

using namespace std;

/** FUNCTION PROTOTYPING **/
void fractionCalc(); //main algorithm
void assignValues(string, int&, int&, int&, int&, char&); //for assigning values (integers and operator)
bool isProperFormat(string); //checks if input is in proper format
bool isOperator(char); //checks if the user gave a proper operator (+, -, *, or /)
bool isNotZero(char); //makes sure a char isn't 0, used to avoid diving by 0 error
void addFrac(int, int, int, int); //adds 2 fractions together
void subtractFrac(int, int, int, int); //subtracts 2 fractions
void multiplyFrac(int, int, int, int); //multiplies 2 fractions
void divideFrac(int, int, int, int); //divides 2 fractions

/** MAIN FUNCTION **/
int main() {
    fractionCalc(); //call to fractionCalc function
    return 0;
}

void fractionCalc()
{
    int frac1num, frac1den, frac2num, frac2den; //integer declarations
    char oprtr; //character delcarion
    bool quit = false; //boolean declaration for quitting
    string equation; //string declaration

    do{
        cout << "Enter a common fraction problem (q to quit): "; //sentence to print to screen at the beginning of each loop
        getline(cin, equation); //get string form user until enter is pressed, set it to string, equation

        if(isProperFormat(equation)) //checks if sentence is format: x/y [operator] a/b
        {
            assignValues(equation, frac1num, frac1den, frac2num, frac2den, oprtr); // if passes check, assignes values

            if(oprtr == '+') //in case of addition
                addFrac(frac1num, frac1den, frac2num, frac2den); //call to addFrac function

            if(oprtr == '-') //in case of subtraction
                subtractFrac(frac1num, frac1den, frac2num, frac2den); //call to subtractFrac function

            if(oprtr == '*') //in case of multiplication
                multiplyFrac(frac1num, frac1den, frac2num, frac2den); //call to multiplyFrac function

            if(oprtr == '/') //in case of division
                divideFrac(frac1num, frac1den, frac2num, frac2den); //call to divideFrac function

        }else if (equation == "q" || equation == "Q") //if string given is sumply "q" or "Q"
            quit = true; //set boolean flag for quitting to "true"

    }while(!quit); //loop until quit flag is set to true

}

bool isProperFormat(string equation)
{
    /** CONDITIONS **/
    if(isdigit(equation[0]) && //first char must be integer from 0-9
       equation[1] == '/' && //second char must be a forwardslash
       isdigit(equation[2]) && //third char must be a digit
       isNotZero(equation[2]) && //third char cannot be 0 (to avoid dividing by 0)
       isspace(equation[3]) && //fourth char must be a space
       isOperator(equation[4]) && //fifth char must be an operator (+, -, *, /)
       isspace(equation[5]) && //sixth char must be a space
       isdigit(equation[6]) && //seventh char must be a digit
       equation[7] == '/' && //eighth char must be a forwardslash
       isdigit(equation[8]) && //ninth char must be a digit
       isNotZero(equation[8])) //ninth char cannot be 0 (to avoid dividing by 0)
    {
        return true; //if all conditions passed, it is in the proper format
    }
    else //if not in proper format
    {
        if(!isOperator(equation[4]) && equation != "q" && equation != "Q") //check if operator was wrong
            cout << "Error: Invalid operator" << endl; //tell user the operator is invalid

        if(equation != "q" && equation != "Q") //if it didn't pass and it wasn't because the user quit
            cout << "Cannot solve this problem." << endl; //give error

        return false; //equation isn't proper format, return flase
    }
}

bool isOperator(char character)
{
    if(character == '+' || //character is + or
       character == '-' || //character is - or
       character == '*' || //character is * or
       character == '/')   //character is /
    {
        return true; //the character is a valid operator
    }
    else //otherwise
    {
        return false; //the character isn't a valid operator
    }
}

bool isNotZero(char number)
{
    if(number != '0') //if character is not equal to 0
        return true; //character is not zero
    else //otherwise
        return false; //character is zero
}

void assignValues(string str, int& frac1num, int& frac1den, int& frac2num, int& frac2den, char& oprtr)
{
    frac1num = str[0] - '0'; //set value of fraction 1 numerator to first value of given string
    frac1den = str[2] - '0'; //set value of fraction 1 denominator to third value of given string
    frac2num = str[6] - '0'; //set value of fraction 2 numerator to seventh value of given string
    frac2den = str[8] - '0'; //set value of fraction 2 denominator to ninth value of given string
    oprtr = str[4]; //set operator to fifth value of given string
}

void addFrac(int frac1num, int frac1den, int frac2num, int frac2den)
{
    if(frac1den == frac2den) //if denominators of 2 given fractions are the same
    {
        cout << "The result of the addition is " << frac1num + frac2num << "/" << frac1den << endl; //print out solution
    }
    else
    {
        int denominator = frac1den * frac2den; //set common denominator
        int numerator1 = frac1num * frac2den; //multiply fraction 1 numerator by fraction 2 denominator
        int numerator2 = frac2num * frac1den; //multiply fraction 2 numerator to fraction 1 denominator

        cout << "The result of the addition is " << numerator1 + numerator2 << "/" << denominator << endl; //print out solution

    }
}

void subtractFrac(int frac1num, int frac1den, int frac2num, int frac2den)
{
    if(frac1den == frac2den) //if denominators of 2 given fractions are the same
    {
        cout << "The result of the subtraction is " << frac1num - frac2num << "/" << frac1den << endl; //print out solution
    }
    else
    {
        int denominator = frac1den * frac2den; //set common denominator
        int numerator1 = frac1num * frac2den; //multiply fraction 1 numerator by fraction 2 denominator
        int numerator2 = frac2num * frac1den; //multiply fraction 2 numerator to fraction 1 denominator

        cout << "The result of the subtraction is " << numerator1 - numerator2 << "/" << denominator << endl; //print out solution

    }
}

void multiplyFrac(int frac1num, int frac1den, int frac2num, int frac2den)
{
    cout << "The result of the multiplication is " << frac1num * frac2num << "/" << frac1den * frac2den << endl; //multiply numerators, multiply denominators, print out solution (num/den)
}

void divideFrac(int frac1num, int frac1den, int frac2num, int frac2den)
{
    cout << "The result of the division is " << frac1num * frac2den << "/" << frac1den * frac2num << endl; //cross multiply, print out solution
}