XNA Game-Themed CS1 Examples (XGC1) Release 2.0 (XNA V3.1) 2/8/2010
Topic: Topic.4.DecisionStructures
Example: Ex_11.LogicalOr

# Decision Statements: Logical OR Operator

References:

• Pre-requisite: it is assumed that you have read through the prior tutorials, and are familiar with the concepts covered in those tutorials.

Goals:

• Throughout this chapter, we will work towards a simple game, with each tutorial adding a little bit more to what we've already done.  In this tutorial, we're going to
1. Refactor our code to use the logical OR operator

1. Obtain the example code

Download and unzip the zip file and you will see an ExampleProgram folder. Open the ExampleProgram folder, the EXE folder contains the compiled program and you can double click on the .sln file to work with the source code.

When the game starts, you'll see a screen that looks similar to this:

The game behaves in a manner that is identical to the what was described for the previous tutorial.  In this tutorial, we will simply refactor some code so that it uses the logical OR operator.

2. Refactoring BounceOffPaddles To Use The Logical OR

• BounceOffPaddles: /// /// Test collision between the soccer ball and the two paddles, /// if collide flip ball's velocity X-component, and keep track /// of number of bounces. /// private void BounceOffPaddles() {     if (m_RightPaddle.Collided(m_TheSoccer) || m_LeftPaddle.Collided(m_TheSoccer))     {         m_TheSoccer.VelocityX = -m_TheSoccer.VelocityX;         PlayACue("Bounce");         if (m_NumBounces > BOUNCES_NEEDED_TO_WIN && m_BallsMissed >= MAX_BALLS_MISSED_TO_WIN)             m_BallsMissed--;         else             m_NumBounces = m_NumBounces + 1;     } }
• If you look back at the BounceOffPaddles function in previous tutorials, you'll notice that no matter which paddle the ball bounces off of, the program does the exact same thing.  Instead of duplicating that code twice, let's refactor that code, and combine the two separate cases into one:
In other words, if the right paddle has collided with the soccer ball, OR the left paddle has collided with the soccer ball, then do everything inside the curly-braces (which you've seen already)

FURTHER EXERCISES::

1. Start from a blank starter project (1000.201, if you need it), and re-do the code from memory as much as possible.  On your first try, do what you can, and keep the above code open so that when you get stuck, you can quickly look up what you forgot (and that after you finish a line, so that you can compare your line to the 'correct' line).  On the next try, do the same thing, but try to use the finished code less.  Repeat this until you can type everything, without refering the tutorial's code.
• Repeat this exercise daily for several days, so that you really get the hang of this.  As you go on, periodically review this by re-doing this exercise.
2. Logical OR
For this exercise, you should use the same project that was explained in the above tutorial.
Looking at the code for the BounceOffBlocks method, is it possible to replace the three separate if statements with a single if statement and several logical ORs, like so:

if (m_ABlock.Collided(m_TheSoccer) || m_BBlock.Collided(m_TheSoccer)  || m_CBlock.Collided(m_TheSoccer) )
{ // more code goes here

Why, or why not?
3. Logical OR vs. Logical AND
For this exercise, you should use the same project that was explained in the above tutorial.
In UpdateWorld, why do we need to use the logical AND, rather than OR, to detect if the player has won?  What would the game play like if we used OR instead?
4. Logical OR
For this exercise, you should use the same project that was explained in the above tutorial.
Change the program so that the game will be reset if the player presses the A button, or if the player presses the B button.