2.11 Conditional Expressions

There are many operations in which the result is dependent on a specific test. For example, the mathematical function \(|x|\), which computes the absolute value of \(x\), is equivalent to the symmetric of \(x\) if \(x\) is negative, and to \(x\) itself otherwise. Using the mathematical notation we have:

\[|x|= \begin{cases} -x, & \text{if $x<0$}\\ x, & \text{otherwise.} \end{cases}\]

This function needs to test if the argument is negative in order to choose one of two alternatives: it either evaluates for the number itself or for its symmetrical value.

Expressions whose result depends on one or more tests are called conditional expressions.

2.11.1 Logical Expressions

A conditional expression follows the structure “if expression then ..., otherwise ...”. The expression that determines whether to use the branch “if” or the branch “otherwise”, is called a logical expression and is characterized for having its value interpreted as either true or false. For example, the logical expression x < 0 tests if the value of x is less than zero; if it is, the expression’s evaluation will return true, otherwise it will return false.

2.11.2 Logical Values