Class Crib Notes for CPSC 110 Brent Dingle

Monday, February 25, 2002

Reminders:

Quiz Wed., Feb. 27

Review:

Still going through procedures

New Stuff for today

More procedures

Some Key Words to watch for:

Global Variables, Local Variables, Scope, Formal Parameters, Actual Parameters, Variable Parameters, Value Parameters, Parameter List

Last time our procedures were using global variables. This is bad. Very bad.
 
So we want to send parameters to the procedures instead. Notice a couple things:

• Both GetName and SayHello would need parameters for first name and last name
• GetName would need to be able to ALTER the contents of parameters (i.e. set them to what the user enters)
• SayHello would NOT need to alter them.

If a procedure can alter a given parameter that parameter is called a VARIABLE PARAMETER.

If a procedure cannot alter a given parameter that parameter is called a VALUE PARAMETER.

So now let’s write that program:

PROGRAM ProcEx3;

VAR

first_name, last_name : string;

{ notice the VAR in front of the variable name means VARIABLE parameter }

{ notice also the variable names duplicate the global var names – they don’t have to }

PROCEDURE GetName(VAR first_name : string; VAR last_name : string);

BEGIN

write(‘Please enter your first name -> ‘);

readln(first_name);

write(‘Please enter your last name -> ‘);

readln(last_name);

END;

{ Note: there is no VAR before either variable name, note also the names are NOT the

same as the global names }

PROCEDURE SayHello(fname : string; lname : string);

BEGIN

writeln(fname, lname, ‘… such a nice name.’);

writeln(‘You must be a great person.’);

END; { end of proc Message }

BEGIN { main body }

WHILE (true) DO

Begin

GetName(first_name, last_name); { note we MUST send first_name first and last_name second }

SayHello(first_name, last_name); { else we will get them mixed around Bob Smith becomes Smith Bob }

End;

END.

Next time

More procedures.