Selection Control Structures

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.

References

  1. Wikipedia: Conditional (computer programming)↵
  2. Wikipedia: Conditional (computer programming)↵

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