assignment

#assignment

##Syntax An assignmentStatement is:

variableReference := expn

##Description An assignment statement calculates the value of the expression (expn) and assigns that value to the variable (variableReference).

##Example

    var i : int
    i := 24         % Variable i becomes 24
    var a : array 1 .. 25 of string
    a (i) := "Ralph"        % The i-th element of a becomes "Ralph"
    �
    var b : array 1 .. 25 of string
    b := a          % Array b becomes (is assigned) array a

##Details The expression on the right of := must be assignable to the variable on the left. For example, in the above, any integer value, such as 24, is assignable to i, but a real value such as 3.14 would not be not assignable to i. Entire arrays, records and unions can be assigned. For example, in the above, array a is assigned to array b. See assignability for the exact rules of allowed assignments.

You cannot assign a new value to a constant (const).

There are short forms that allow you to write assignment statements more compactly. For example,

i := i + 1

can be shortened to

i += 1

In Turing, there are short forms for combining +, = and * with assignment. For example, i *= 2 doubles i.

There are also short forms to allow any binary operator to be combined with assignment. For example, i shl= 2 shifts i by 2 to the left.