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Conditional statements control whether a part of a script is executed depending the result of a particular expression (i.e whether an expression returns a boolean ''true'' or ''false'' value). The two types of conditional structures are ''if'' and ''if ... else''. In this section we will take a closer look at both of these condtional structures and provide some examples of their use.

The first line of an 'if'' structure involves the ''if'' statement followed by the expression to be evaluated in parentheses. For example: