Codes below…

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 WindowsFormsApplication2
{
public partial class pizza : Form
{

//Some global strings to keep radiobutton and checkbox events text's.
private String a1 = null;
private String a2 = null;
private String a3 = null;
private String menu = null;

public pizza()
{
InitializeComponent();
}

private void button1_Click(object sender, EventArgs e)
{

// This event for new order button, so it makes everything null.
textBox1.Text = null;
textBox2.Text = null;
radioButton1.Checked = false;
radioButton2.Checked = false;
radioButton3.Checked = false;
checkBox1.Checked = false;
checkBox2.Checked = false;
checkBox3.Checked = false;
}

private void button3_Click(object sender, EventArgs e)
{
Application.Exit(); // it used for exit button
}

private void button2_Click(object sender, EventArgs e)
{
String name = textBox1.Text;
String surname = textBox2.Text;

MessageBox.Show("Name: " + name + "\nSurname: " + surname + "\nMenu: " + menu + "\nAdditions:" + a1 + a2 + a3, "Confirm Your Order!", MessageBoxButtons.YesNo ,MessageBoxIcon.Information);

}

private void checkBox1_CheckedChanged(object sender, EventArgs e)
{
if (checkBox1.Checked)
{
a1 = " Mushroom";
}
else
{
a1 = null;
}
}

private void checkBox2_CheckedChanged(object sender, EventArgs e)
{
if (checkBox2.Checked)
{
a2 = " Olive";
}
else
{
a2 = null;
}
}

private void checkBox3_CheckedChanged(object sender, EventArgs e)
{
if (checkBox3.Checked)
{
a3 = " Corn";
}
else
{
a3 = null;
}
}

private void radioButton1_CheckedChanged(object sender, EventArgs e)
{
menu = "Classic";
}

private void radioButton2_CheckedChanged(object sender, EventArgs e)
{
menu = "Full";
}

private void radioButton3_CheckedChanged(object sender, EventArgs e)
{
menu = "Vegeterian";
}
}
}

Any questions ?

Here as you see from the screenshot of the main window a user should guess the result of this operation. Textbox1 equals the random number “96″, textbox2 equals the random number “73″ and there is an randomly operator which is “-” . User should guess this result and should write down the guess into the textbox3 field. When user press enter button textbox3 handles this event.

private void textBox3_KeyPress(object sender, KeyPressEventArgs e)
{
if (e.KeyChar == (char)13) //Char 13 handles the enter key
{
Console.WriteLine(total);  //Here i can check the result from console for testing purposes
if (total.ToString() == textBox3.Text)
{
StringBuilder dogru_str = new StringBuilder();
dogru_str.Append(textBox1.Text);
dogru_str.Append(" " + label1.Text + " ");
dogru_str.Append(textBox2.Text + " = ");
dogru_str.Append(total + "\n");
dogru_str.Append("Your answer was correct...");
MessageBox.Show(dogru_str.ToString(), "Result", MessageBoxButtons.OK, MessageBoxIcon.Asterisk);

Here dogru_str keeps the new string. Then  i am able to send this paramater to MessageBox.Show

wins += 1; //Here i can show that how many times user wins
label4.Text = wins.ToString();
textBox3.ReadOnly = true;
}
else
{
StringBuilder yanlis_str = new StringBuilder();
yanlis_str.Append(textBox1.Text);
yanlis_str.Append(" " + label1.Text + " ");
yanlis_str.Append(textBox2.Text + " = ");
yanlis_str.Append(total + "\n");
yanlis_str.Append("Your answer was wrong.!!");
MessageBox.Show(yanlis_str.ToString(), "Result", MessageBoxButtons.OK, MessageBoxIcon.Error);
loses += 1;
label5.Text = loses.ToString();
textBox3.ReadOnly = true;
}
}
}  

After pressing enter button it determines if it is wrong answer or not. Then user should press replay button the replay the game.

…

private int RandomNumber(int min, int max)
{
Random random = new Random();
int rand = random.Next(min, max);
return rand;
}

I need to convert this interger number to a string. And this function takes to parameters minimum & maximum. That helps you to determine the interval of this random numbers.

//Determine about operator
String[] operators = { "+", "-", "/", "*" };
int rand3 = random.Next(1, 5);
//Console.WriteLine(rand3.ToString());
switch (rand3.ToString())
{
case "1":
label1.Text = "+";
total = rand1 + rand2;
break;
case "2":
label1.Text = "-";
total = rand1 - rand2;
break;
case "3":
label1.Text = "/";
total = rand1 / rand2;
break;
case "4":
label1.Text = "*";
total = rand1 * rand2;
break;
default:
label1.Text = "Error";
break;
}

Here i put a switch as an example. It gives me a random number and then i am able to get a random char from my string array.