Class Crib Notes for CPSC 110 Brent Dingle

Monday, March 18, 2002

Notices:

For those that missed class on Friday before Spring Break – no new material was presented.

An attendance extra credit bonus was assigned to those who attended.

Lab assignment 5 is due Monday and Tuesday, March 25 and 26.

You will have a quiz next Wednesday, March 27.

Midterm exams should be returned today and tomorrow (March 18, 19).

There was a 2% curve on the exam.

There is an opportunity to have an additional 2% added to the midterm – see the webpage.

Recall that you MUST turn in a short history report as detailed in the syllabus (and on the webpage) under handouts before the last regular class period (April 30).

Review:

Memorize this: ONLY variables may be sent as variable parameters.

For Today:

This is all in chapter 5 (refresh yourselves with local, global, scope, block)

Today we will be discussing functions. Here are the key points to remember:

• Functions take arguments.
• Procedures take parameters.
• Arguments are just another word for parameters.
• Functions should NOT output anything.
• Functions return EXACTLY one value.
• Functions should NOT alter the value of any of their parameters/arguments.
• Thus the parameters/arguments to a function should all be VALUE parameters.
  They don’t have to be – they just SHOULD be.
• The format for a function is:

FUNCTION FunctionName( parameter list) : return_type;

VAR

local variables declared

BEGIN

body of the function

FunctionName := some value; ß This is how the function returns a value

The last value assigned to the function name is the value

returned

END;

• So inside the body of the function the function name MUST appear on the LEFT hand side of the assignment operator at least once.
• Inside the body of the function the function name MAY NOT appear on the RIGHT hand side of the assignment operator.
• To CALL A FUNCTION you will in the MAIN BODY say something like:
  variable_name := FunctionName( whatever, arguments, are, needed );
  This will set variable_name equal to whatever value the function returns.
  Like in:
  x := sin(theta);

Example – Function which returns the CUBE of a number:

PROGRAM CubeIt;

VAR

x, x_cubed : real;

FUNCTION Cube( z : real ); { notice z is a formal VALUE parameter }

VAR

local_v : real;

BEGIN

local_v := z * z * z;

Cube := local_v; { This line is what determines what value the function returns}

END;

BEGIN { main body }

x := 5;

x_cubed = Cube(x);

Writeln(‘The cube of ’, x, ‘ is ’, x_cubed);

END.

Doing the same thing with a procedure we would have had to use TWO parameters and one of them would need to be a VARIABLE parameter. So the procedure which does the same thing as the function Cube above would be:

PROGRAM CubeIt2;

VAR

x, x_cubed : real;

PROCEDURE ProcCube( z : real; var v : real );

VAR

local_v : real;

BEGIN

local_v := z * z * z;

v := local_v;

END;

BEGIN { main body }

x := 5;

ProcCube(x, x_cubed);

Writeln(‘The cube of ’, x, ‘ is ’, x_cubed);

END.