Programming Fundamentals/Selection Control Structures

From Wikibooks, open books for an open world
Jump to navigation Jump to search


In selection control structures, conditional statements perform different computations or actions depending on whether a programmer-specified Boolean condition evaluates to true or false.[1]


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[edit]

The if then else control structure is a two-way selection.

If age > 17
    Output "You can vote."
    Output "You can't vote."
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[edit]

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."
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[edit]

if then else
A two-way selection control structure.
A multi-way selection control structure.