Parameters

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By default, parameters are passed by value, which means the function or procedure operates on a local copy of the variable used in the parameter list.  The original variable in the call will not be changed by the procedure or function. Example:

procedure Test(s: string);
begin
  s := s + 'More Characters';
end;

var
  MyString : string;
begin
  MyString := 'Hello';
  Test( MyString );
  writeln( MyString ); {MyString was not changed by what happened in Test}
end;

However, parameters can be passed by reference so that the original variable is changed.  To pass a variable by reference, use the keyword var in the procedure's or function's parameter list.  Example:

procedure Test(var s: string);
begin
  s := s + 'More Characters';
end;

var
  MyString : string;
begin
  MyString := 'Hello';
  Test( MyString );
  writeln( MyString ); {Now, MyString will be changed by the Test procedure}
end;

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