4.2: Selection Control Structures
- Page ID
- 10655
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In selection control structures, conditional statements are features of a programming language which perform different computations or actions depending on whether a programmer-specified Boolean condition evaluates to true or false.[1]
Discussion
The basic attribute of a selection control structure is to be able to select between two or more alternate paths. This is described as either two-way selection or multi-way selection. A question using Boolean concepts usually controls which path is selected. All of the paths from a selection control structure join back up at the end of the control structure, before moving on to the next lines of code in a program.
If Then Else Control Structure
The if then else control structure is a two-way selection.
If age > 17
Output "You can vote."
False:
Output "You can't vote."
End
| Language | Reserved Words |
|---|---|
| C++ | if, else |
| C# | if, else |
| Java | if, else |
| JavaScript | if, else |
| Python | if, elif, else |
| Swift | if, else |
Case Control Structure
The case control structure is a multi-way selection. Case control structures compare a given value with specified constants and take action according to the first expression to match.[2]
Case of age
0 to 17 Display "You can't vote."
18 to 64 Display "You're in your working years."
65 + Display "You should be retired."
End
| Language | Reserved Words |
|---|---|
| C++ | switch, case, break, default |
| C# | switch, case, break, default |
| Java | switch, case, break, default |
| JavaScript | switch, case, break, default |
| Python | N/A |
| Swift | switch, case, break (optional), default |
Python does not support a case control structure. There are workarounds, but they are beyond the scope of this book.
Key Terms
- if then else
- A two-way selection control structure.
- case
- A multi-way selection control structure.