Operators

Introduction

An operator in a programming language is a symbol that tells the compiler or interpreter to perform a specific mathematical, relational or logical operation and produce a final result.

C has many powerful operators. Many C operators are binary operators, which means they have two operands. For example, in a / b, / is a binary operator that accepts two operands (a, b). There are some unary operators which take one operand (for example: ~, ++), and only one ternary operator ? :.

Syntax

• expr1 operator
• operator expr2
• expr1 operator expr2
• expr1 ? expr2 : expr3

Remarks

Operators have an arity, a precedence and an associativity.

• Arity indicates the number of operands. In C, three different operator arities exist:
• Unary (1 operand)
• Binary (2 operands)
• Ternary (3 operands)
• Precedence indicates which operators “bind” first to their operands. That is, which operator has priority to operate on its operands. For instance, the C language obeys the convention that multiplication and division have precedence over addition and subtraction:

a * b + c

Gives the same result as

(a * b) + c

If this is not what was wanted, precedence can be forced using parentheses, because they have the highest precedence of all operators.

a * (b + c)

This new expression will produce a result that differs from the previous two expressions.

The C language has many precedence levels; A table is given below of all operators, in descending order of precedence.

Precedence Table

Operators                                                     | Associativity
------                                                        | ------
(), [], ->, .                                                 | left to right
!, ~, ++, --, +, -, * (dereference), (type), sizeof           | right to left
* (multiplication), /, %,                                     | left to right
+, -                                                          | left to right
<<, >>                                                        | left to right
<, <=, >, >=                                                  | left to right
==, !=                                                        | left to right
&                                                             | left to right
^                                                             | left to right
|                                                             | left to right
&&                                                            | left to right
||                                                            | left to right
?:                                                            | right to left
=, +=, -=, *=, /=, %=, &=, ^=, |=, <<=, >>=                   | right to left
,                                                             | left to right

• Associativity indicates how equal-precedence operators binds by default, and there are two kinds: Left-to-Right and Right-to-Left. An example of Left-to-Right binding is the subtraction operator (\-). The expression

a - b - c - d

has three identical-precedence subtractions, but gives the same result as

((a - b) - c) - d

because the left-most \- binds first to its two operands.

An example of Right-to-Left associativity are the dereference \* and post-increment ++ operators. Both have equal precedence, so if they are used in an expression such as

* ptr ++

, this is equivalent to

* (ptr ++)

because the rightmost, unary operator (++) binds first to its single operand.