Rules of Operator Precedence

C++ applies the operators in arithmetic expressions in a precise order determined by the following rules of operator precedence, which are generally the same as those in algebra:

1. Operators in expressions contained within pairs of parentheses are evaluated first. Parentheses are at the highest level of precedence. In cases of nested, or embedded, parentheses, such as

the operators in the innermost pair of parentheses are applied first.

2. Multiplication, division and modulus operations are applied next. If an expression contains several multiplication, division and modulus operations, operators are applied from left to right. Multiplication, division and modulus are on the same level of precedence.

3. Addition and subtraction operations are applied last. If an expression contains several addition and subtraction operations, operators are applied from left to right. Addition and subtraction also have the same level of precedence.

The rules of operator precedence define the order in which C++ applies operators. When we say that certain operators are applied from left to right, we are referring to the associativity of the operators. For example, the addition operators (+) in the expression

associate from left to right, so a + b is calculated first, then c is added to that sum to determine the whole expression’s value. We’ll see that some operators associate from right to left. Figure 2.7 summarizes these rules of operator precedence. We expand this table as we introduce additional C++ operators. Appendix A contains the complete precedence chart.

Fig. 2.7. Precedence of arithmetic operators.