CHAPTER 4 - SELECTION CONTROL STRUCTURES

Abstract

This chapter explains the uses of simple selection, multiple selection, and nested selection in algorithms. The structure represents the decision making abilities of the computer. That is, a programmer would use the selection control structure in pseudocode to illustrate a choice between two or more actions, depending on whether a certain condition is true or false. There are a number of variations of the selection structure. Simple selection occurs when a choice is made between two alternative paths, depending on the result of a condition being true or false. The structure is represented in pseudocode using the keywords IF, THEN, ELSE, and ENDIF. Nested selection occurs when the word IF appears more than once within an IF statement. Nested IF statements can be classified as linear or nonlinear. Each variation of the selection structure developed in pseudocode can similarly be represented using a Nassi-Schneiderman diagram. The case structure was introduced as a means of expressing a linear nested IF statement in a simpler and more concise form. Case is available in many high level languages, and so is a useful construct to write in pseudocode.