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 (
b). There are some unary operators which take one operand (for example:
++), and only one ternary operator
- expr1 operator
- operator expr2
- expr1 operator expr2
- expr1 ? expr2 : expr3
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 <code>|</code> | left to right `&&` | left to right <code>||</code> | left to right `?:` | right to left `=` `+=` `-=` `*=` `/=` `%=` `&=` `^=` <code>|=</code> `<<=` `>>=` | 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.