C Pocket Reference

Assignment Operators

Assignments are performed by simple and compound assignment operators, as shown in Table 1-10.

Table 1-10. Assignment operators

Operator	Meaning	Example	Result
=	Simple assignment	x = y	Assign the value of y to x
op=	Compound assignment	x += y	x op= y is equivalent to x = x op (y) (where op is a binary arithmetic or binary bitwise operator)

The left operand in an assignment must be an lvalue; i. e., an expression that designates an object. This object is assigned a new value.

The simplest examples of lvalues are variable names. In the case of a pointer variable ptr, both ptr and *ptr are lvalues. Constants and expressions such as x+1, on the other hand, are not lvalues.

The following operands are permissible in a simple assignment (=):

• Two operands with arithmetic types

• Two operands with the same structure or union type

• Two pointers that both point to objects of the same type, unless the right operand is the constant NULL

If one operand is a pointer to an object, then the other may be a pointer to the “incomplete” type void (i. e., void *).

If the two operands have different types, the value of the right operand is converted to the type of the left operand.

An assignment expression has the type and value of the left operand after the assignment. Assignments are grouped from right to left. For example:

a = b = 100;  // equivalent to  a=(b=100); 
              // The value 100 is assigned to b and a.

A compound assignment has the form x op= y, where op is a ...