programming-for-dummies

Chapter 4: Making Decisions
by Branching
In This Chapter
Using the IF-THEN, IF-THEN-ELSE, and IF-THEN-ELSEIF statements
Using multiple Boolean operators
Using the SELECT CASE statement
The simplest program lists commands one after another in a sequence,
much like following the steps of a recipe. Follow a recipe step by step
and you always create the same dish. If a program lists commands step by
step, the computer always produces the same result.
In some cases, you may want a program to do the exact same thing over and
over again, such as a simple program to display traffic signals. However for
most programs, you want the computer to react to outside data. To make a
computer respond in different ways, a program needs to offer two or more
choices for the computer to follow.
When you quit a program, the program may ask, “Do you really want to
exit?” At this point, the program is giving the computer a choice of two possible
actions to take based on your answer.
If you answer Yes, the computer quits the program. If you answer No, the
computer keeps running the program.
When a program gives the computer a choice of two or more commands to
follow, that’s called a branching or decision statement.
All branching statements work the same way:
✦ A comparison operator (or a conditional expression) compares an
expression (such as A > 45) to determine a True or False value.
✦ The branching statement offers at least two groups of commands for
the computer to follow based on whether its comparison is True or
False.