6 Arithmetic

Arithmetic operators in C attempt to be as similar as possible to the abstract arithmetic operations, but it is impossible to do this perfectly. Numbers in a computer have a finite range of possible values, and non-integer values have a limit on their possible accuracy. Nonetheless, in most cases you will encounter no surprises in using ‘+’ for addition, ‘-’ for subtraction, and ‘*’ for multiplication.

Each C operator has a precedence, which is its rank in the grammatical order of the various operators. The operators with the highest precedence grab adjoining operands first; these expressions then become operands for operators of lower precedence. We give some information about precedence of operators in this chapter where we describe the operators; for the full explanation, see Binary Operator Grammar.

The arithmetic operators always promote their operands before operating on them. This means converting narrow integer data types to a wider data type (see Operand Promotions). If you are just learning C, don’t worry about this yet.

Given two operands that have different types, most arithmetic operations convert them both to their common type. For instance, if one is int and the other is double, the common type is double. (That’s because double can represent all the values that an int can hold, but not vice versa.) For the full details, see Common Type.