✏️ Explanatory Question
In programming, especially when working with assignment statements, the terms
l-value and r-value are used to describe the
roles played by expressions on the left-hand side and right-hand side of an
assignment operator (=).
An l-value (left value) is an expression that refers to a specific memory location and can generally appear on the left-hand side of an assignment statement. In simple terms, an l-value identifies the destination where a value can be stored.
A variable is a common example of an l-value because it represents a modifiable storage location.
x = 10
In this statement, x is the l-value because it
represents the location where the value 10 is stored.
An r-value (right value) is an expression that provides a value to be assigned, used, or evaluated. It normally appears on the right-hand side of an assignment operator.
In the following example:
x = 10
10 is the r-value because it is the value that
is assigned to x.
a = 20
b = a + 5
In the first statement, a is the l-value and 20
is the r-value.
In the second statement, b is the l-value, while
a + 5 is the r-value because the expression is evaluated to
produce a value that is assigned to b.
| l-value | r-value |
|---|---|
| Usually appears on the left side of an assignment. | Usually appears on the right side of an assignment. |
| Represents a storage location. | Represents a value or expression that produces a value. |
| Can generally receive a value. | Provides a value to be used or assigned. |
Example: x |
Example: 10, x + 5 |
10 = x
This is invalid because 10 is a literal value and does not
represent a modifiable storage location. Therefore, it cannot act as an
l-value in a normal assignment.
Similarly, an expression such as x + 5 generally cannot be
used as the destination of an assignment because it produces a value rather
than identifying a modifiable storage location.
You can remember the difference using this simple rule:
l-value = Where the value is stored
r-value = The value that is stored or used
Therefore, in total = price + tax,
total is the l-value, while
price + tax is the r-value.