Constants and switch statement? - C++ beginner programming

[lisagimros]

Hi.
I'm doing an assignment for school and it says that I must use constants for the menu choices. And I must use constants for Mets values and I also must use a switch statement. I don't know what any of that means.. I would ask my professor but I don't have class until next week.. The program runs perfectly and does what it is supposed to do, which is to work like a calorie calculator. However, I have to follow the exact instructions. Anyone who could try to explain to me what I have to do to follow those instructions? Here is my code so far:

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

int main()
{

    float weightInPounds, mets, mins, totalCal, calPerMinute;

    cout << "Hello and Welcome to the Calorie Calculator!\n";

    // Prompting the user to enter weight
    cout << "Please Enter Your Weight in Pounds: " << endl;
    cin >> weightInPounds;


    // Prompting the user to enter number of mets
    cout << "Please select your exercise:" << endl;
    cout << "1. Running" << endl;
    cout << "2. Basketball" << endl;
    cout << "3. Sleeping" << endl;
    cout << "4. Quit" << endl;

    int choice;
    cin >> choice;

    if (choice == 1)
        mets = 10;

    else if  (choice == 2)
        mets = 8;

    else if (choice == 3)
        mets = 1;

    else if (choice == 4)
        cout << "See you next time!" << endl;

    else
        cout << "Invalid selection" << endl;


    // Prompting the user to enter the duration
    cout << "Enter the Duration in Minutes: " << endl;
    cin >> mins;

    // Adding two decimals to the results
    cout << fixed << setprecision (2);

    // Calculating the total amount of calories burned
    calPerMinute = 0.0175 * (weightInPounds / 2.2) * mets;
    totalCal = calPerMinute * mins;

    // Displaying the results
    cout << "You burned an estimated " << totalCal << " calories." << endl;

    return 0;

[JLBorges]

#include <iostream>
#include <iomanip>

int main()
{
    // use constants for Mets values
    const int Mets_Running = 10 ;
    const int Mets_Basketball = 8 ;
    const int Mets_Sleeping = 1 ;

    std::cout << "Hello and Welcome to the Calorie Calculator!\n\n" ;

    // Prompting the user to enter weight
    std::cout << "Please Enter Your Weight in Pounds: " ;
    double weightInPounds = 0 ;
    std::cin >> weightInPounds;
    if( weightInPounds <= 0 )
    {
        std::cout << "invalid weight\n" ;
        return 1 ; // non-zero to indicate failure
    }

    std::cout << "Please select your exercise:\n"
              << "1. Running\n"
              << "2. Basketball\n"
              << "3. Sleeping\n"
              << "4. Quit\n\n"
              << "? " ;

    int choice = 0 ;
    std::cin >> choice ;

    double mets = 0 ;

    // use a switch statement (replace the if - else if construct)
    // see switch statement (bottom of the page) in
    // http://www.cplusplus.com/doc/tutorial/control/
    switch(choice)
    {
        case 1: mets = Mets_Running ; break ; // 1. Running

        case 2: mets = Mets_Basketball ; break ; // 2. Basketball

        case 3: mets = Mets_Sleeping ; break ; // 3. Sleeping

        case 4: std::cout << "See you next time!\n" ; break ; // 4. Quit

        default: std::cout << "Invalid selection\n" ; return 1 ;
    }

    if( mets > 0 ) // if running, basketball or sleeping
    {
        // Prompting the user to enter the duration
        std::cout << "Enter the Duration in Minutes: " ;
        int mins = 0 ;
        std::cin >> mins;

        if( mins > 0 ) // valid non-zero duration
        {
            const double calPerMinute = 0.0175 * ( weightInPounds / 2.2 ) * mets ;
            const double totalCal = calPerMinute * mins;
            std::cout << "\nYou burned an estimated " << std::fixed
                      << std::setprecision (2) << totalCal << " calories.\n" ;
        }
    }

    // there is an implicit return 0 ; at the end of main
}