Trying some shit and learning

//chapter 1
//Make it Fancy

//Included Library Files
//needed for cin, cout, endl
#include <iostream>
//needed for system("pause");
#include <stdlib.h>
//for numeric_limits
#include <limits>
//needed for the random number generator
#include <time.h>
//needed for getchar
#include <stdio.h>

//using Declarations
using std::cout;
using std::endl;
using std::cin;
using std::numeric_limits;
using std::streamsize;

/*this is like declaring a variable, except we're declaring a void function called GameOver*/
void GameOver();
void ExpensiveCalculator();
void GameStats();
void NumberGame();
int intcheck(int x);
char yncheck(char main);



//Starting the Main Program
int main()
{
    char menu = 'y';
    int choice;

    do
    {
        system("Color 0F");
        cout << "Your Options are: ";
        cout << "\n1 - Expensive Calculator ";
        cout << "\n2 - Game Stats";
        cout << "\n3 - Number Guessing Game";
        cout << "\n4 - Game Over";
        cout << "\nPlease Select an option: ";
        cin >> choice;
        choice = intcheck(choice);

        if (choice == 1)
        {
        /*This calls the void function ExpensiveCalculator(), the program jumps to void ExpensiveCalculator() and executes the entire function.*/
        ExpensiveCalculator();
        cout << endl << endl;
        system("pause");
        } //return a value to show successful run of main program

        else if (choice == 2)
        {
        /*This calls the void function GameStats, the program jumps to void GameStats() and executes the entire function.*/
        GameStats();
        system("pause");
        cout << endl << endl;
        }
        else if (choice == 3)
        {
        NumberGame();
        system("pause");
        cout << endl << endl;
        }
        else if (choice == 4)
        {
        /*This calls the void function GameOver, the program jumps to void GameOver() and executes the entire function.*/
        GameOver();
        cout << endl << endl;
        system("pause");
        }
        else
        {
           cout << "Invalid Input\n\n";
        }

        cout << "Return to main Menu (y/n):";
        cin >> menu;
        menu = yncheck(menu);

        system("CLS");
    } while (menu =='y');
    //return a value to show successful run of main program
    return 0;
}

/*This is the void function itself, this is what runs when GameOver() is called */
void GameOver()
{
    system("Color 1B");
    system("CLS");
    cout << "\t\t\tOk, Bye!\n";
    cout << "#############################################################" << endl;
    cout << "#                    _                                      #" << endl;
    cout << "#                  -=\\`\\                                    #" << endl;
    cout << "#              |\\ ____\\_\\__                                 #" << endl;
    cout << "#            -=\\c`\"\"\"\"\"\"\" \"`)                               #" << endl;
    cout << "#               `~~~~~/ /~~`\                                #" << endl;
    cout << "#                 -==/ /                                    #" << endl;
    cout << "#                   '-'                                     #" << endl;
    cout << "#                  _  _                                     #" << endl;
    cout << "#                 ( `   )_                                  #" << endl;
    cout << "#                (    )    `)                               #" << endl;
    cout << "#              (_   (_ .  _) _)                             #" << endl;
    cout << "#                                             _             #" << endl;
    cout << "#                                            (  )           #" << endl;
    cout << "#             _ .                         ( `  ) . )        #" << endl;
    cout << "#           (  _ )_                      (_, _(  ,_)_)      #" << endl;
    cout << "#         (_  _(_ ,)                                        #" << endl;
    cout << "#############################################################" << endl;
    cout << "\t\t\tSee you later!!\n" << endl;
    cout << " Please report Errors to Will. \n\n";
    cout << "Game Over!" << endl;
}

/*This is the void function itself, this is what runs when ExpensiveCalculator() is called */
void ExpensiveCalculator()
{
    system("CLS");
    float first, second;
    int intfirst, intsecond;
    cout << "Please Enter your First Number and press enter: ";
    cin >> first;
    cout << "Please Enter your Second Number and press enter: ";
    cin >> second;
    intfirst = first;
    intsecond = second;
    cout << first << " + " << second << " = " << first + second << endl;
    cout << first << " - " << second << " = " << first - second << endl;
    cout << first << " * " << second << " = " << first * second << endl;
    cout << first << " / " << second << " = " << first / second << endl;
    //not needed previous line does the same thing
    //cout << "7.0 / 3.0 = " << 7.0 / 3.0 << endl;
    cout << intfirst << " % " << intsecond << " = " << intfirst % intsecond << endl;
    cout << first << " + " << second << " * 5 = " << first + second * 5 << endl;
    cout << first << "(" << first << " + " << second << ") * 5 = " << (first + second) * 5 << endl;
}

void GameStats()
{
    system("CLS");
    int score;
    double distance;
    char playAgain;
    bool shieldsUp;

    short lives, aliensKilled;

    score = 0;
    distance = 1200.76;
    playAgain = 'y';
    shieldsUp = true;
    lives = 3;
    aliensKilled=10;

    double engineTemp = 6572.89;

    cout << "\nScore: " << score << endl;
    cout <<"Distance: " << distance <<endl;
    cout <<"Play Again: " << playAgain << endl;
    //Skipping shields up
    cout << "Lives :" << lives << endl;
    cout << "Aliens Killed: " << aliensKilled << endl;
    cout << "Engine Temp: " << engineTemp << endl;

    int fuel;
    cout << "\nHow Much Fuel?";
    cin >> fuel;
    fuel = intcheck(fuel);

    cout << "Fuel: " << fuel << endl;

    typedef unsigned short int ushort;
    ushort bonus = 10;
    cout << "\nBonus: " << bonus <<
     endl;
}
void NumberGame()
{
    //Initialize and assign values to variables, and get the number generator working.
    srand(time(0));
    int secretnumber;
    int tries = 0;
    int guess;
    char again = 'y';
    bool bFail;

    system("CLS");

    //Change Color Again
    system("Color 1F");

    //Welcome Screen for number game
    cout << "\n\nWelcome to Guess The Number \n";
    cout << "Possible answer range is from 1 to 100.\n\n\n";

    //Main game loop, will loop while (again == y) allowing for multiple plays
    while (again == 'y')
    {
        //Set secretnumber to a random number between 1 and 100
        secretnumber = rand() % 100 + 1;

        //Loop to allow for multiple guesses
        do
        {
            //Get input, verify input is an integer.
            do
            {
                cout << "Enter your guess: ";
                cin >> guess;
                //checking cin to make sure it is infact and interger,loops till interger is input
                guess = intcheck(guess);

                //Checking to make sure input is between 1 and 100
                while (guess > 100 || guess <= 0)
                {
                    cout << "Guess must be a number from 1 to 100. Please enter your guess: ";
                    cin >> guess;
                    //checking cin to make sure it is infact and interger,loops till interger is input, clear out extra inputs
                    bFail = cin.fail();
                    cin.clear();
                    cin.ignore(numeric_limits<streamsize>::max(), '\n');
                }

            } while (bFail == true);

            //increment try countersystem("CLS");
            ++tries;

            //Too high notification
            if (guess > secretnumber)
            {
                cout << "Too High! \n\n";
            }

            //Too low notification
            else if (guess < secretnumber)
            {
                cout << "Too Low! \n\n";
            }

            //Correct answer notification as well as output for number of tries
            else
            {
                cout << "\nThat's It! You got it in " << tries << " guesses!\n";
            }

        } while (guess != secretnumber);

        //Ask user if they would like to play again this needs improved in the same way guess input needs improved
        cout << "Play Number Game again (y/n)?: ";
        cin >> again;
        again = yncheck(again);
        //Reset Try counter for next game
        tries = 0;
    }
    cout << "Thanks for Playing My Number Game.\n\n";
}

int intcheck(int xc)
{
    bool inputcheck;
    inputcheck = cin.fail();
    do
    {
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
        cout << "Please enter a valid number: ";
        cin >> xc;
        inputcheck = cin.fail();
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max(), '\n');
    }while (inputcheck == true);
    return xc;
}

char yncheck(char mainc)
{
    bool inputcheck;
    inputcheck = cin.fail();
    do
    {
        cin.clear();
        cin.ignore(numeric_limits<streamsize>::max(), '\n');

        while (mainc != 'y' && mainc != 'n')
        {
            cout << "Please enter y or n:";
            cin >> mainc;
            //checking cin to make sure it is infact and interger,loops till interger is input, clear out extra inputs
            inputcheck = cin.fail();
            cin.clear();
            cin.ignore(numeric_limits<streamsize>::max(), '\n');
        }
    }while (inputcheck == true);
    return mainc;

}