Menu Driven Program to convert MKS to CGS and CGS to MKS

// C++ menu-driven program using the Switch case
// to convert the CGS system to MKS system
// and vice versa

#include <iostream>
using namespace std;

// declare mks class pre-hand for reference
// to mks class for friend function in cgs.
class mks;

class cgs {

private:
    // cgs units: centimeter, gram, second.
    //(length, weight, time)
    float cm, gm, sec;

public:
    // Default constructor
    cgs()
    {
        cm = 0;
        gm = 0;
        sec = 0;
    }

    // Parameterized constructor
    cgs(float x, float y, float z)
    {
        cm = x;
        gm = y;
        sec = z;
    }

    void disp_cgs()
    {
        cout << cm << "\t" << gm
             << "\t" << sec << "\n";
    }

    void disp_cgs1()
    {
        cout << cm;
    }

    void disp_cgs2()
    {
        cout << gm;
    }

    void disp_cgs3()
    {
        cout << sec;
    }

    // friend functions:
    friend mks cgs2mks(cgs);
    friend cgs mks2cgs(mks);
};

class mks {

private:
    // mks units: meter, kilogram, second.
    //(length, weight, time)
    float m, kg, sec;

public:
    // Default constructor
    mks()
    {
        m = 0;
        kg = 0;
        sec = 0;
    }

    // Parameterized constructor
    mks(float x, float y, float z)
    {
        m = x;
        kg = y;
        sec = z;
    }

    void disp_mks()
    {
        cout << m << "\t" << kg
             << "\t" << sec << "\n";
    }

    void disp_mks1()
    {
        cout << m;
    }

    void disp_mks2()
    {
        cout << kg;
    }

    void disp_mks3()
    {
        cout << sec;
    }

    friend mks cgs2mks(cgs);
    friend cgs mks2cgs(mks);
};

// mks->cgs conversion:
mks cgs2mks(cgs c)
{
    mks t;
    t.m = c.cm / 100;
    t.kg = c.gm / 1000;
    t.sec = c.sec;
    return t;
}

// cgs->mks conversion:
cgs mks2cgs(mks d)
{
    cgs t;
    t.cm = d.m * 100;
    t.gm = d.kg * 1000;
    t.sec = d.sec;
    return t;
}

// Code for menu
void menu(int mainMenuChoice, int parameterChoice)
{
    float distanceValue = 30, weightValue = 300, timeValue = 3000;
    int continueChoice = 0;

    cout << "MKS <-> CGS converter menu:\n";
    do {
        cout << "Enter 1 for CGS to MKS conversion.\n"
             << "Enter 2 for MKS to CGS conversion.\n";

        cout << "\nYou have chosen: "
             << mainMenuChoice
             << "\n\n";

        switch (mainMenuChoice) {

        case 1: {
            cout << "Enter 0 to convert all three parameters"
                 << "- distance, weight and time.\n"
                 << "Enter 1 for converting distance\n"
                 << "Enter 2 for converting weight\n"
                 << "Enter 3 for converting time\n";

            cout << "\nYou have chosen: "
                 << parameterChoice
                 << "\n\n";

            switch (parameterChoice) {
            case 0: {
                cout << "Enter values for distance unit in centimeter.\n";
                distanceValue;
                cout << endl;
                cout << "Enter values for weight unit in grams.\n";
                weightValue;
                cout << endl;
                cout << "Enter values for time unit in seconds.\n";
                timeValue;
                cout << endl;

                cout << "The entered values in CGS system are: \n";
                cgs c(distanceValue, weightValue, timeValue);

                c.disp_cgs();

                cout << "Corresponding values in MKS system: \n";
                mks m = cgs2mks(c);

                m.disp_mks();

                cout << endl;
                break;
            }

            case 1: {

                cout << "Enter values for distance unit in centimeter.\n";
                distanceValue;
                cout << endl;

                cout << "The entered values in CGS system are: \n";
                cgs c(distanceValue, 0, 0);

                c.disp_cgs();

                cout << "Corresponding values in MKS system: \n";
                mks m = cgs2mks(c);

                m.disp_mks();

                cout << endl;
                break;
            }
            case 2: {

                cout << "Enter values for weight unit in grams.\n";
                weightValue;
                cout << endl;

                cout << "The entered values in CGS system are: \n";
                cgs c(0, weightValue, 0);

                c.disp_cgs();

                cout << "Corresponding values in MKS system: \n";
                mks m = cgs2mks(c);

                m.disp_mks();

                cout << endl;
                break;
            }
            case 3: {

                cout << "Enter values for time unit in seconds.\n";
                timeValue;
                cout << endl;

                cout << "The entered values in CGS system are: \n";
                cgs c(0, 0, timeValue);

                c.disp_cgs();

                cout << "Corresponding values in MKS system: \n";
                mks m = cgs2mks(c);

                m.disp_mks();

                cout << endl;
                break;
            }
            }
            break;
        }

        case 2: {
            cout << "Enter 0 to convert all three parameters"
                 << "- distance, weight and time.\n"
                 << "Enter 1 for converting distance\n"
                 << "Enter 2 for converting weight\n"
                 << "Enter 3 for converting time\n";

            cout << "\nYou have chosen: "
                 << parameterChoice
                 << "\n\n";

            switch (parameterChoice) {
            case 0: {
                cout << "Enter values for distance unit in meter.\n";
                distanceValue;
                cout << endl;
                cout << "Enter values for weight unit in kilogram.\n";
                weightValue;
                cout << endl;
                cout << "Enter values for time unit in second.\n";
                timeValue;
                cout << endl;

                cout << "The entered values in MKS system are: \n";
                mks m(distanceValue, weightValue, timeValue);

                m.disp_mks();

                cout << "Corresponding values in CGS system: \n";
                cgs c = mks2cgs(m);

                c.disp_cgs();

                cout << endl;
                break;
            }

            case 1: {
                cout << "Enter values for distance unit in meter.\n";
                distanceValue;
                cout << endl;

                cout << "The entered values in MKS system are: \n";
                mks m(distanceValue, 0, 0);

                m.disp_mks();

                cout << "Corresponding values in CGS system: \n";
                cgs c = mks2cgs(m);

                c.disp_cgs();

                cout << endl;
                break;
            }

            case 2: {

                cout << "Enter values for weight unit in kilogram.\n";
                weightValue;
                cout << endl;

                cout << "The entered values in MKS system are: \n";
                mks m(0, weightValue, 0);

                m.disp_mks();

                cout << "Corresponding values in CGS system: \n";
                cgs c = mks2cgs(m);

                c.disp_cgs();

                cout << endl;
                break;
            }

            case 3: {

                cout << "Enter values for time unit in second.\n";
                timeValue;
                cout << endl;

                cout << "The entered values in MKS system are: \n";
                mks m(0, 0, timeValue);

                m.disp_mks();

                cout << "Corresponding values in CGS system: \n";
                cgs c = mks2cgs(m);

                c.disp_cgs();

                cout << endl;
                break;
            }
            }
        }
        }
        cout << "Enter 1 to continue, or\n"
             << "Press any other key to exit.\n";

    } while (continueChoice == 1);
}

// Driver code
int main()
{

    cout << "Check for CGS to MKS of all units.\n\n";
    menu(1, 0);

    cout << "\n-------------------------------------------------\n";

    cout << "\nCheck for CGS to MKS of only distance unit.\n\n";
    menu(1, 1);

    cout << "\n-------------------------------------------------\n";

    cout << "\nCheck for CGS to MKS of only weight unit.\n\n";
    menu(1, 2);

    cout << "\n-------------------------------------------------\n";

    cout << "\nCheck for CGS to MKS of only time unit.\n\n";
    menu(1, 3);

    cout << "\n-------------------------------------------------\n";

    cout << "Check for MKS to CGS of all units.\n\n";
    menu(2, 0);

    cout << "\n-------------------------------------------------\n";

    cout << "\nCheck for MKS to CGS of only distance unit.\n\n";
    menu(2, 1);

    cout << "\n-------------------------------------------------\n";

    cout << "\nCheck for MKS to CGS of only weight unit.\n\n";
    menu(2, 2);

    cout << "\n-------------------------------------------------\n";

    cout << "\nCheck for MKS to CGS of only time unit.\n\n";
    menu(2, 3);

    cout << "\n-------------------------------------------------\n";

    return 0;
}