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Things we have learned:
- Not every single line of code we write will always be executed. We can use if/else statements to allow conditional execution of code. We do this when sometimes we want to have something (a method) happen, and sometimes we don't. An example of a condition might be if one object is "close enough" to another object.
- if/else statements use a Boolean expression (a special type of mathematical expression that evaluates to one of two values: true or false) to control when code is executed. It has a place to put code to execute when the expression is true, and a place to put code to execute when the expression is false. (However, you do not always have to put code in the false part).
- There are a number of ways to describe boolean conditions. In Alice (and some other programming languages) we frequently use <, <=, >, >=, ==, !=.
Questions you should be able to answer after this module:
[Q8.6.1] How would you change the boolean expression below if you wanted this code to have the Angel move to the Egyptian only when the Angel was more than 3 meters away from the Egyptian.
[Q8.6.2] How would you change the boolean expression below if you wanted this code to have the Angel move to the Egyptian only when the Angel was exactly 1 meter in height?
[Q8.6.3] Write an if statement that has an Egyptian say "Hello down there" when he is more than 3 meters tall and otherwise have him say "I want to grow up".
[Q8.6.4] True or false: When a boolean expression controlling an if statement evaluates to false, you do both the code right after the "if" and the code after the "else".
Example:
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