C++ Primer, Fifth Edition

5.3.1. The if Statement

An if statement conditionally executes another statement based on whether a specified condition is true. There are two forms of the if: one with an else branch and one without. The syntactic form of the simple if is

if (condition)     statement

An if else statement has the form

if (condition)     statementelse     statement2

In both versions, condition must be enclosed in parentheses. condition can be an expression or an initialized variable declaration (§ 5.2, p. 174). The expression or variable must have a type that is convertible (§ 4.11, p. 159) to bool. As usual, either or both statement and statement2 can be a block. ...