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## 6.4 Parentheses for Grouping

Any expression wrapped in parentheses is also an expression. Like in C++, but unlike in R, only the round parentheses, ( and ), are allowed. The square brackets [ and ] are reserved for array indexing and the curly braces { and } for grouping statements.

With parentheses it is possible to explicitly group subexpressions with operators. Without parentheses, the expression 1 + 2 * 3 has a subexpression 2 * 3 and evaluates to 7. With parentheses, this grouping may be made explicit with the expression 1 + (2 * 3). More importantly, the expression (1 + 2) * 3 has 1 + 2 as a subexpression and evaluates to 9.