Latest revision as of 06:26, 4 January 2015

Operators in C follow strict precedence rules defined by the C standard. The table below lists C language operators in order of precedence from highest to lowest.

Operators[edit]

Expressions[edit]

An expression is a sequence of operators, operands, object designators, or functions that specifies computation of a value. An object's stored value may only be modified once between any two sequence points. This is important to watch out for because it means the following are undefined:

x = ++x + 1;
arr[x++] = x;
++x = ++x;

While allowing the following:

x = x + 1;
arr[x] = x;
x = ++x;

is well defined.

Precedence and Evaluation[edit]

Precedence are rules used to define the order of binding in a sequence of expressions where they are not explicitly specified by a pair of parentheses. For example in,

++x+3*4

The table indicates that x is bound more tightly to ++ than to the + operator. Likewise, 3 is bound more tightly to * than to +. Therefore it is equivalent to:

((++x)+(3*4))

or

(++x, x+(3*4))

It's important to note that the actual order of evaluation is independent of precedence or associativity. In fact, the order of evaluation of subexpressions and the order in which side is evaluated is unspecified behavior by the C standard.

This means that in the following line,

x = f(1) + f(2) + f(3);

The function calls f(1), f(2), and f(3) may be called in any order. You may not assume that f(1) will be called before f(2) or f(3).