Visual Basic.NET How to Program (PDF)

Chapter 5 Control Structures: Part 2 145
Henri Bergson
Outline
5.1 Introduction
5.2 Essentials of Counter-Controlled Repetition
5.3 For/Next Repetition Structure
5.4 Examples Using the For/Next Structure
5.5 Select Case Multiple-Selection Structure
5.6 Do/Loop While Repetition Structure
5.7 Do/Loop Until Repetition Structure
5.8 Using the Exit Keyword in a Repetition Structure
5.9 Logical Operators
5.10 Structured Programming Summary
Summary Terminology Self-Review Exercises Answers to Self-Review Exercises Exercises
5.1 Introduction
Before writing a program to solve a particular problem, it is essential to have a thorough
understanding of the problem and a carefully planned approach to solving it. It is equally
essential to understand the types of building blocks available and to employ proven program-construction
principles. In this chapter, we discuss these issues in conjunction with
our presentation of the theory and principles of structured programming. The techniques
we explore are applicable to most high-level languages, including Visual Basic. In Chapter
8, Object-Based Programming, we show how the control structures we present in this
chapter are useful in the construction and manipulation of objects.
5.2 Essentials of Counter-Controlled Repetition
In the last chapter, we introduced the concept of counter-controlled repetition. In this section,
we formalize the elements needed in counter-controlled repetition, namely:
1. The name of a control variable (or loop counter) that is used to determine whether
the loop continues to iterate.
2. The initial value of the control variable.
3. The increment (or decrement) by which the control variable is modified during
each iteration of the loop, or each time the loop is performed).
4. The condition that tests for the final value of the control variable (i.e., whether
looping should continue).
The example in Fig. 5.1 uses the four elements of counter-controlled repetition to display
the even digits from 2–10.
The declaration in line 8 names the control variable (counter), indicates that it is of
data type Integer, reserves space for it in memory and sets it to an initial value of 2. This