having the ball,

//all others not having the ball

//set up the current player variable currentPlayer = playerNumber;

//show no player with ball for(int i = 0; i < 5; i++){

picPlayer[i].BorderStyle = BorderStyle.None; picPlayer[i].Image = myPics.Images[2];

} // end for loop

//reset goalie image picPlayer[GOALIE].Image = myPics.Images[5];

//show current player holding ball picPlayer[playerNumber].BorderStyle =

BorderStyle.FixedSingle; picPlayer[playerNumber].Image = myPics.Images[3];

}// end setPlayer

Before I set up the visual representation of the player with the ball, I ensure that the preceding player is shown without the ball. The easiest way to do this is to set all the players without the ball. A player without the ball is represented by image 2 of the image list and has no border. The goalie image (if he doesn’t have the ball) is image 5 of the image list. When all the images are clear, I set the border style of the current player to a fixed single−line border, and I set the image to image 3 of the image list, which shows the player with the ball.

Trick At first, I just used the ball to indicate which player had the ball, but the ball is so tiny that it is hard to spot. I added the border as an easy way to determine which player currently has the ball. Many sports games do something similar to ease gameplay.

Handling the Passage of Time

The program has a timer control used to pace the game. When the timer ticks, three things happen. The clock is updated, showing how many seconds are left of playing time. The player picture boxes are moved randomly, and the opponent picture boxes are also moved randomly. It shouldn’t surprise you that each of these three tasks is relegated to a method, the updateTime(), movePlayers(), and moveOpp() methods.

private void timer1_Tick(object sender, System.EventArgs e) {

updateTime();

movePlayers();

moveOpp();

} // end timerTick

Again, encapsulation comes to the rescue. The timer_tick() method calls three other methods to do all the work, but it’s easy to see from the tick method exactly which tasks occur whenever the timer ticks.

Updating the Clock

The first task is to update the clock. This seems quite simple, and it is, but merely reporting how much time is left is not enough. At some point, the user will be out of time, and the game will have to

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end. The code to handle the end of the game is called inside the updateTime() method:

private void updateTime(){ //calculate time left timeLeft−−;

if (timeLeft <=0){ timer1.Enabled = false;

DialogResult playAgain = MessageBox.Show ("Game Over. Play Again?", "Soccer",

MessageBoxButtons.YesNo);

if (playAgain == DialogResult.Yes){ //start over

playerScore = 0; oppScore = 0; timeLeft = 600;

currentPlayer = FULLBACK; updateScore(); timer1.Enabled = true;

}else {

// end game Application.Exit();

}// end playAgain if

}else {

double totalSeconds = timeLeft/10;

int minutes = (int) (totalSeconds /60); int seconds = (int) (totalSeconds % 60);

string timeString = minutes.ToString() + ":

"+ seconds.ToString();

lblTime.Text = timeString;

} // end if

}// end updateTime

The first order of business is to decrement the timeLeft variable. This variable started out at 600, and it will be decremented by 1 each time the timer ticks. Because the timer is set at an interval of 10 frames per second, timeLeft will be 0 after 60 seconds. If timeLeft is less than or equal to 0, time has expired. In this situation, I display a dialog box asking whether the user wants to play again. If so, I reset all the key variables (score, time left, and current player variables) and restart the timer. If not, I end the application.

If the value of timeLeft is larger than 0, I do some quick math to determine how many minutes and seconds are left and then send this value to the user.

Trick Notice how I use the % operator to determine the number of seconds. This is called the modulus operator. It comes in handy in a number of situations, but many people don’t know about it. The modulus operator returns the remainder of a long division problem. For example, if totalSeconds had the value 63, minutes would get the value 61 divided by 60, or 1 with a remainder of 3. If you divide two integers, the result is an integer, which completely ignores the remainder value. You can use the modulus operator to get the remainder of a division problem.

The minutes and seconds are stored as integers, so I reformatted them to send them to the time label.

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Moving the Players

Part of this game's appeal is the way the little players run around on the field. To be honest, the movement of the players has absolutely no effect on the outcome of the game as it is currently set up. However, the action does add appeal, and you could change the code so that the distance between a player and the goal is the major determinate of the likelihood the player will score. (Hmmm, sounds like another good exercise.) All player motion is entirely random, as you can see from the code:

private void movePlayers(){ //move players

int motion;

Random roller = new Random();

for (int i = 1; i < 5; i++){ motion = roller.Next(11) − 5; picPlayer[i].Left += motion; motion = roller.Next(11) −5; picPlayer[i].Top += motion;

//check for boundaries

if (picPlayer[i].Left < 0){ picPlayer[i].Left = 0;

}else if (picPlayer[i].Left + picPlayer[i].Width > pnlField.Width){

picPlayer[i].Left = pnlField.Width − picPlayer[i].Width;

}else if (picPlayer[i].Top < 0){ picPlayer[i].Top = 0;

}else if (picPlayer[i].Top + picPlayer[i].Height > pnlField.Height){

picPlayer[i].Top = pnlField.Height − picPlayer[i].Height;

}// end if

}// end for loop

}// end movePlayers

I set up a for loop to go one at a time through each player (except the goalies—they don’t move).

I used a random integer named motion to determine how much the player would move. I played with the motion variable to get exactly the effect I was looking for. The solution I settled on calls for grabbing a number between 0 and 10 and then subtracting 5 from that number. This results in a random value between –5 and 5.

Trap My first thought was to use the two−integer version of the random object’s Next() method to extract a value in the range I wanted. However, when I experimented with that approach, I found that the numbers were not as random as I wanted. They tended to be negative far more often than positive. This caused all my players to drift toward one corner of the field, which was not the behavior I was looking for. There’s a lesson here. You can try to find methods and objects that make your life easier, but you still have to test. If they don’t do what you want, you must figure out another way.

I added motion to the Left property of the player, recalculated motion using the same formula, and added it to the Top property. The net effect is that each element moves up to 5 pixels in each

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direction randomly each time the timer ticks, making the nice random motion of players on the screen.

As you’ve heard by now, whenever you increment or decrement a variable, you should check for boundary conditions. In this case, this means making sure that the players don’t move off the field. I did this by comparing the player’s position with the field panel.

Moving the Opponents

The motion of the opponents is very much like that of the players. In fact, all I did was copy the code and change the picture box name to picOpp.

Hint Usually, when you find yourself copying code, it’s an indicator that you should modify your data structure. I decided not to in this case because although the motion of the opponents and the players is identical, players and opponents are different in many other aspects, so they should still be different arrays.

private void moveOpp(){ //move opponents

int motion;

Random roller = new Random();

for (int i = 1; i < 5; i++){ motion = roller.Next(11) − 5; picOpp[i].Left += motion; motion = roller.Next(11) −5; picOpp[i].Top += motion;

//check for boundaries if (picOpp[i].Left < 0){

picOpp[i].Left = 0;

}else if (picOpp[i].Left + picOpp[i].Width > pnlField.Width){

picOpp[i].Left = pnlField.Width − picOpp[i].Width;

}else if (picOpp[i].Top < 0){ picOpp[i].Top = 0;

}else if (picOpp[i].Top + picOpp[i].Height > pnlField.Height){

picOpp[i].Top = pnlField.Height − picOpp[i].Height;

}// end if

}// end for loop

}// end moveOpp

As in the player movement scheme, the position of the opponents has no bearing on the game play. In fact, the opposing players are completely unnecessary. They are just there for visual effect.

Updating the Score

Updating the score is an easy chore, but because it’s done from several places, it is a good candidate for a method call:

private void updateScore(){ lblPlScore.Text = "Player: " +

playerScore.ToString(); lblOppScore.Text = " Opp: " +

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