Understanding the concept of 1 to 1 relationship, and applying it to C#

Given the constraint that one object (Player) cannot exist without another object (Play Game), a one-to-one relationship representation in C# would mean that only one game per player, and without any game, we cannot have any player (makes perfect sense).

Tutorial to set up the One-to-One relationship
1) Set up the one-to-one relationship
Create your two independent forms (Form1 and Form2 by default) by adding them to your project in Visual Studio.
Now, you need to create a dependency between those two forms. I am using forms Game (Form1) and Player (Form2).

In Player (Form2) form where you would usually declare your fields,

//fields
//create the dependency to Game Form
private Game myGameForm;

Apply the same logic to the Form1 class, or the Game class.

//fields
//create the dependency to Play Form
private Play myPlayForm;

2) Create the dependency that Form2 cannot exist without Form1.

We want the Play object to exist only if we have a Game.

//fields
//create the dependency to Play Form
private Play myPlayForm;

public Game()
{
    myPlayForm = new Play(this);//create a Play form if the game exists
    InitializeComponent();
}

Obviously, we cannot have a player if we do not have the game. To enforce this constraint, we make use of the constructor for the Form2, so that Form2 (or Game), will only be created if a Form1 object (Game) is not passed as an argument to the constructor.

//fields
//create the dependency to Game Form
private Game myGameForm;

public Play(Game gameform)
{
    InitializeComponent();
    myGameForm = gameform;//assign the object myGameForm to the argument gameform
}

So what did we exactly do? We said that if a Game exists, then the player also exists.

3) Show the second Form2 (Player) when the button on Form1 (Game) is clicked.

private void btnPlay_Click(object sender, EventArgs e)
{
    myPlayForm.Show();
}

Run your code. On clicking the button from Form1 (Game), you will see the new form Player appear. You're on the right track. That's all we need to know to assign 1-to-1 dependency with constraints!

End of Tutorial


This was the first part of the question. The rest is very easy and will require the use of Random. I've included the full code of the application below.

The Game Class

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace OneToOne
{
    public partial class Game : Form
    {
        //fields
        //create the dependency to Play Form
        private Play myPlayForm;

        //constructor
        public Game()
        {
            myPlayForm = new Play(this);//create a Play form if the game exists
            InitializeComponent();
        }

        //events
        private void btnPlay_Click(object sender, EventArgs e)
        {
            myPlayForm.Show();
        }

        //methods
        public void showValue(int maxval)
        {
            lblMax.Text = "Max Number is " + maxval.ToString()+ ".\n\nRestart game to play again";
        }
    }
}

The Play Class

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace OneToOne
{
    public partial class Play : Form
    {
        //fields
        //create the dependency to Game Form
        private Game myGameForm;
        private int myNum = 0;
        private int iCounter = 0;

        //properties
        public int MyNum
        {
            get { return myNum; }
            set { myNum = value; }
        }

        public int ICounter 
        {
            get { return iCounter; }
            set { iCounter = value; }
        }

        //constructor
        public Play(Game gameform)
        {
            InitializeComponent();
            myGameForm = gameform;  //assign the object myGameForm to the argument gameform
        }

        //events
        private void btnClick_Click(object sender, EventArgs e)
        {
            showValue();
        }

        //methods
        public void showValue()
        {
            Random myRan = new Random();    //create a myRan variable of type Random (Class)
            int iRan = myRan.Next(100); //gets a random number from 0 - 100
            iCounter++;

            if (iCounter <= 3)   //can click only 3 times
            {
                lblNum.Text = iRan.ToString();  //display random value on form
                if (iRan >= myNum)
                {
                    myNum = iRan;
                }
            }
            else
            {
                MessageBox.Show("Cannot click more than 3 times. Turn has ended");
                //prevent user from clicking more than 3 times
                btnClick.Enabled = false;

                //send the max value to Form1 or GameForm
                myGameForm.showValue(myNum);
                //hide this form
                this.Hide();

                //show the previous form
                myGameForm.Show();

            }
        }
    }
}

I hope that helps!