High-level Programming Language (Pascal)

Assignment Statements

• gives a value or computational result to a variable
• the syntax of an assignment statement is

  <variable> := <expression>

  • <expression> may be a constant value, another variable already holding a value or a formula to be evaluated
  • := is known as the assignment operator (means 'gets the value of ')
  • no space between a colon (:) and an equal sign (=)
    
    
• the expression on the right hand side is evaluated first, then the result is stored in the variable on the left
• once a variable is assigned a new value, the previous value, if any, will be replaced or overwritten by the new value
• the expression must be assignment compatible (e.g. of the same data type) with the variable identifier
• it is legal to assign an integer value to a real variable, the integer value will be converted to the corresponding real value
• it is not legal to assign a real value to an integer variable
• the following are examples of invalid Pascal assignment statements with reasons

  var Number : integer;
  　　Code : char;
  　　Found : boolean;
  

  Statement	Error
  5 := Number;	variable must appear on the left of the assignment operator
  Number+3.5 := 2.7;	arithmetic expressions may not appear on the left of the assignment operator
  Code := 5;	numeric value may not be assign to a character variable
  Number := '5';	character constant may not be assigned to a numeric variable
  Number := 3.4;	real value may not be assigned to an integer variable
  Number :='2'+'3';	'2'+'3' is not a legal expression
  Found := 'false'	'false' is not a Boolean expression