while Loop and Keyboard

A while loop repeats the following block of statements while the given condition is true.

This program prints the square of each natural number i while the square is smaller than 300.

The condition of the while loop is checked only at the beginning of each iteration.

After running the program, modify it so that it also outputs the value of variable i on each iteration.

After that, modify the program so that it outputs the first 123 squares of natural numbers. Since the program needs to output a long list, make the program run faster. To verify that the list is correct, check that the last number in the list ends with digits 129.

	while i <= 123 

This program increases the variable i until the Esc key is pressed.

Run the program, and then use the Escape key to end it.

Change the println statement in the loop into a following statement: println "i: ", i.atmost(13);

Then, try to figure out what is the purpose of the getter atmost.

Then, try changing the inserted statement to use the getter atleast instead of atmost.

* * *

Note for touchscreen users only: you can try changing the condition of the while loop into not isPressed("touch").

This is a variation of the previous program. It clears the screen by calling the clearScr function on each iteration of the while loop.

After running the program, modify it so that it prints out the square of variable i on the end of program execution.

This program draws a disc at the horizontal position i.

The result is a simple animation.

After running and studying the program, change the third argument (the literal 100) of the disc function call to some other value and observe how it affects the output. Try values 20 and 200.

Exercise 1

Modify the program so that the disc increases in size while moving.

disc(i, 200, i/4, /red);

After that, change the second argument (i.e. literal 200) to some other value and observe how it affects the output. Try values 600 and 300.

Exercise 2

Modify the program so that the disc moves vertically, in a direction from the top to the bottom.

disc(200, i, 100, /red);

This program changes the color of the disc when an appropriate key is pressed.

* * *

Note for touchscreen users only:
try with:
isPressed("touch1") (one-finger touch)
and
isPressed("touch2") (two-finger touch)
.

This program moves a disc when the left or right arrow key is pressed.

Movement is explained in more detail in chapter on animations.

Exercise 1

Try insering an if statement in order to prevent the x coordinate getting smaller than 50. This will prevent the disc from moving outside the left side of screen.

Exercise 2

Reload the original program. Try using the getter atleast to prevent the x coordinate getting smaller than 50.

This program displays the name of the last key pressed.

This program can be used to find out the names of keyboard keys.

This program also displays whether a key is pressed or not.

Run the program and test it. Then, use the Escape key to end it.

After executing the program, modify it by using an if statement so that the program displays a text "A key is pressed" while any key is pressed.

The condition of the while loop is always true, therefore the loop never ends.

That makes an infinite loop. It cannot ever end, so the program keeps executing forever.

The 'Exit' button can end such programs immediately.

Run the program, and then use the 'Exit' button to terminate the program.

Note that the final statement will never be executed, therefore it can be deleted from the source code.

This program uses a do-while loop. The condition of a do-while loop is verified only at the end of each iteration. Therefore, a do-while loop is guaranteed to perform at least one iteration.

A do-while loop repeats a sequence of statements. A statement block is not required.

* * *

* * *