Converting to Boolean

As you’ve seen, an if statement works by performing an evaluation of a condition. The program “branches” to one place or another depending on whether the condition evaluates to the Boolean value of true or false.

However, the types placed in the condition that’s evaluated aren’t restricted to the Boolean type. This means that it’s safe to use any type for a Boolean evaluation in a conditional statement as long as you realize that the implicit conversion forced by the evaluation will follow the rules shown in Table 3-1.

Table 3-1: Conversion to Boolean


Converts to Boolean Value As Follows


Converts to false


Converts to false if 0, –0, +0, or NaN; otherwise, true


Converts to false if the string length = 0; otherwise, converts to true


Converts to false

Try This at Home

As a puzzle, try constructing if statements that rely on the conversions shown in Table 3-1 —and verify that the conversions work in the way that I’ve said they do.

Learn How to Program Using Any Web Browser
Learn How to Program Using Any Web Browser
ISBN: 1590591135
EAN: 2147483647
Year: 2006
Pages: 115
Authors: Harold Davis

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