Learn to Program with C_ Learn to Program using the Popular C Programming Language ( PDFDrive )

Chapter 4
Programs with Selection Logic
In this chapter, we will explain the following:
• What are Boolean expressions
• How C represents Boolean values
• How to write programs using if
• How to write programs using if...else
• Where semicolons are required, where they are optional, and where they
must not be put
• How a program should be tested
• Why symbolic constants are useful and how to use them in a C program
4.1 Introduction
In the last chapter, we showed how to write programs using sequence logic—programs whose
statements are executed “in sequence” from the first to the last.
In this chapter, the programs will use selection logic—they will test some condition and take
different courses of action based on whether the condition is true or false. In C, selection logic is
implemented using the if and the if...else statements.
4.2 Boolean Expressions
A Boolean expression (named after the famous English mathematician George Boole) is one that
is either true or false. The simplest kinds of Boolean expressions are those that compare one value
with another. Some examples are:
k is equal to 999
a is greater than 100
a2 + b2 is equal to c2
b2 is greater than or equal to 4ac
s is not equal to 0
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