Editing Operator associativity (section)

== Right-associativity of assignment operators ==

In many [[imperative programming language]]s, the [[assignment operator]] is defined to be right-associative, and assignment is defined to be an expression (which evaluates to a value), not just a statement. This allows [[Assignment (computer science)#Chained assignment|chained assignment]] by using the value of one assignment expression as the right operand of the next assignment expression.

In [[C (programming language)|C]], the assignment <code>a = b</code> is an expression that evaluates to the same value as the expression <code>b</code> converted to the type of <code>a</code>, with the [[Side effect (computer science)|side effect]] of storing the [[Value (computer science)#lrvalue|R-value]] of <code>b</code> into the [[Value (computer science)#lrvalue|L-value]] of <code>a</code>.{{efn|1=An expression can be made into a [[Statement (programming)|statement]] by following it with a semicolon; i.e. <code>a = b</code> is an expression but <code>a = b;</code> is a statement.}} Therefore the expression <code>a = (b = c)</code> can be interpreted as <code>b = c; a = b;</code>. The alternative expression <code>(a = b) = c</code> raises an error because <code>a = b</code> is not an L-value expression, i.e. it has an R-value but not an L-value where to store the R-value of <code>c</code>. The right-associativity of the <code>=</code> operator allows expressions such as <code>a = b = c</code> to be interpreted as <code>a = (b = c)</code>.

In [[C++]], the assignment <code>a = b</code> is an expression that evaluates to the same value as the expression <code>a</code>, with the side effect of storing the R-value of <code>b</code> into the L-value of <code>a</code>. Therefore the expression <code>a = (b = c)</code> can still be interpreted as <code>b = c; a = b;</code>. And the alternative expression <code>(a = b) = c</code> can be interpreted as <code>a = b; a = c;</code> instead of raising an error. The right-associativity of the <code>=</code> operator allows expressions such as <code>a = b = c</code> to be interpreted as <code>a = (b = c)</code>.