C Pocket Reference

Expressions and Operators

An expression is a combination of operators and operands. In the simplest case, an expression consists simply of a constant, a variable, or a function call. Expressions can also serve as operands, and can be joined together by operators into more complex expressions.

Every expression has a type and, if the type is not void, a value. Some examples of expressions follow:

4 * 512                         // Type: int  
printf("An example!\n")         // Type: int 
1.0 + sin(x)                    // Type: double
srand((unsigned)time(NULL))     // Type: void
(int*)malloc(count*sizeof(int)) // Type: int *

In expressions with more than one operator, the precedence of the operators determines the grouping of operands with operators. The arithmetic operators *, /, and %, for example, take precedence over + and -. In other words, the usual rules apply for the order of operations in arithmetic expressions. For example:

4 + 6 * 512    // equivalent to 4 + (6 * 512)

If a different grouping is desired, parentheses must be used:

(4 + 6) * 512

Table 1-8 lists the precedence of operators.

Table 1-8. Precedence of operators

Priority	Operator	Grouping
1	() [] -> .	left to right
2	! ~ ++ -- + - (type) * & sizeof	right to left
3	* / %	left to right
4	+ -	left to right
5	<< >>	left to right
6	< <= > >=	left to right
7	== !=	left to right
8	&	left to right
9	^	left to right
10	|	left to right
11	&&	left to right
12	||	left to right
13	?:	right to left
14	= += -= *= ...