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The blue block labeled move 90 steps causes the basketball to move 90 steps forward (in the direction that it is facing) . Each step constitutes one unit in the Cartesian coordinate system. For example, if you were to change this value from 90 to 240, thatwould cause the basketball to move from the origin to the extreme right edge of the Stage.
As I indicated earlier , the selection structure is sometimes referred to as a decision structure. In other words, this structure causes the program to select or make a decision between two alternatives. The pseudocode in Image 9 describes this process.
if a specified condition is true
perform a specified actionotherwise (when the specified condition is not true)
perform a different action
Sometimes the second part of the selection process isn't needed. In other words, in some cases, if the specified condition is not true, there is norequirement to do anything at all. That is the case in this program.
This program makes two independent decisions shown by the pseudocode in Image 10 .
if the basketball is touching the beachball on the right
turn around and face to the leftif the basketball is touching the beachball on the left
turn around and face to the right
These two decisions are implemented by the two light tan blocks in Image 8 containing the word if . (From this point forward, I won't distinguish between dark tan and light tan.)
Clicking the tan Control button shown at the upper center in Image 4 exposes a large number of programming blocks. Twoof them are used to create pure selection structures (if-then and if-then-else) and one is used to create a combination of a loop structure and a selection structure (repeat-until).
Clicking the tan Control button shown at the upper center in Image 4 exposes the blocks shown in Image 11 . As mentioned above, two of the blocks can be used tocreate pure selection structures and one can be used to create a combination of a loop structure and a selection structure. The other blocksserve other purposes.
Selection structures are created by dragging the selection blocks into the rightmost panel in order to apply them to a particularsprite.
The if-then-else block in Image 11 is used to select between two specific actions (or two sequences of actions) . The if-then block is used when there is only one action (or one sequence of actions) and you need to decide whether to take that action or not.
That latter case describes the situation in this program. If the basketball is touching a beachball, a specific action is required.If the basketball is not touching a beachball, no specific action is required.
Note the empty darker depressed area in some of the blocks shown in Image 11 (the rectangles with the pointed ends) . In order to use these blocks, you must drop another block having the same shape into the depressedarea. The block that you drop into that area must specify the condition that will be used to make the decision.
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