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

//    The pupose of this program is to prompt user's to enter two
//    numeric values and an operation to be preformed on those two
//    values. The program will then accept the user's input and perform
//    the requested operation and display the original two values, as
//    either sum, difference, product, quotient, exponentiation, or remainder.
//    It is assumed that the program could operate as a more advanced
//    four function calculator.

//    Function prototypes
    char mainMenu();
    double getUserValue(string);
    double addition(double, double);
    double subtraction(double, double);
    double multiplication(double, double);
    double division(double, double);
    void pauseForEnter();
    void exponetiation(double, double, double);
    void modulus(double, double, double);

    int main()
    {
        //    Declare variables
        char operation = ' ';
        double value1  = 0.0;
        double value2  = 0.0;
        double result  = 0.0;
        string keypress = "";

        //    Set numeric format and precisions for numericouput with
        // cout.
        cout << setiosflags(ios::fixed) << setprecision(2);

        //    Begin the main program loop
        do
        {
            //    Call the mainMenu() function to display the menu and
            //    get the user's menu choice.
            operation = mainMenu();

            //    Evaluate the user choice and determine what we need
            //    to do.
            if ((operation == 'A') || (operation == 'S') || (operation
                == 'M') || (operation == 'D')|| (operation == 'Q'))
            {
                //    Get the user values
                value1 = getUserValue("first");
                value2 = getUserValue("second");

                //    Perform the requested operation and display the results.
                switch (operation)
                {
                case 'A': result = addition(value1, value2);
                    printf("Result: %.2f + %.2f = %.2f\n\n", value1, value2, result);
                    break;

                case 'S': result = subtraction(value1, value2);
                    printf("Result: %.2f - %.2f = %.2f\n\n", value1, value2, result);
                    break;

                case 'M': result = multiplication(value1, value2);
                    printf("Result: %.2f * %.2f = %.2f\n\n", value1, value2, result);
                    break;

                case 'D': if (value2 != 0.0)
                          {
                              result = division(value1, value2);
                              printf("Result: %.2f / %.2f = %.2f\n\n", value1, value2, result);
                          }
                          else
                          cout << "\nError: Division by zero is not permitted.\n\n";
                        //    end if/else
                    break;

                case 'E': if (value != 0.0)
                          {
                              result = exponentiation(value1, value2);
                              printf("Result: %.2f < %.2f = %.2f\n\n", value1, value2, result);
                              break;
                          }

                case 'R': if (value != 0.0)
                          {
                              result = Modulus(value1, value2);
                              printf("Results: %.2f < %.2f = %.2f\n\n", value1, value2, result);
                              break;
                        
                }
                //    end switch

            }
            
            else if (operation != 'Q')
                printf("\nError: Invalid operation requested. Operation %c is not defined.\n\n",
                operation);

            else
                cout << "\nGoodbye!\n";
            //    end if/else

           //    Pause the program for keystroke.
                pauseForEnter();
        }
        while (operation != 'Q');
        //    end do while

        //    Terminate the program
        return 0;
    }
    //    end function main()

    //    The function mainMenu() displays an explanation of the purpose of
    //    the program, as well as a menu of choices for the user. The user
    //    choice is obtained and returned to the caller.
    char mainMenu()
    {
        //    Declare variables
        char userChoice = ' ';

        //    Clear the screen, display the menu, and get the user menu
        //    choice.
        system("cls");
        cout << "This program will accept two numeric values and the perform\n"
            << "The desired operation on those values.\n"
            << "\nTo select the desired operation, enter the characters\n"
            << "Associated with the operation as shown below.\n\n";
        cout << "\tA or a - Addition\n";
        cout << "\tS or s - Suntraction\n";
        cout << "\tM or m - Multiplication\n";
        cout << "\tD or d - Division\n";
        cout << "\tQ or q - Quit\n\n";
        cout << "Which operation would you like to perform? ";
        cin >> userChoice;
        cin.clear();

        //    Convert the user to uppercase and return to caller.
        return toupper(userChoice);
    }
    //    end function mainMenu()

    //    The function getUserValue() prompts the user to enter a value
    //    to be used is the operation requested. The value is obtained
    //    and returned to the caller.
    double getUserValue(string whichValue)
    {
        //    Declare variables
        double value = 0.0;

        //    Prompt the user to enter a value and return it to the caller.
        cout << "Enter the " << whichValue << " numeric value:";
        cin >> value;
        cin.clear();

        //    Return the value
        return value;
    }
    //    end function getUserValue()

    //    The function addition() calculates and return the sum of its
    //    parameter
    double addition(double num1, double num2)
    {
        return (num1 + num2);
    }
    //    end function addition

    //    The function subtraction() calculates and return the difference
    //    of its parameter
    double subtraction(double num1, double num2)
    {
        return (num1 - num2);
    }
    //    end function subtraction

    //    The function multiplication() calculates and return the product
    //    of its parameter
    double multiplication(double num1, double num2)
    {
        return (num1 * num2);
    }
    //    end function multiplication

    //    The function division() calculates and return the qoutient
    //    of its parameter
    double division(double num1, double num2)
    {
        return (num1 / num2);
    }
    //    end function division

    //    The function pauseforEnter() waits for the user to press the
    //    (Enter) key.
void pauseForEnter()
{
    //    Declare vaiables
        string keypress = "";

    //    Pause the program for a keystroke
        cout << "Please press (Enter)...";
        cin.ignore (1000,'\n');
        getline(cin, keypress);

    //    The function of exponentiation is to raise a numer x to the next power y
        void exponetiation(double, double, double);


}    //    end program