Modular Programming

1
Modular Programming

• Summer Institute for Computer Studies Teachers
• August 2001

2
From the curriculum

• incorporate modularity into the design process
• write subroutines that pass parameters and use
  local and global variables
• describe the purpose of functions and procedures,
  and how they are expressed in a programming
  language

3
From the curriculum contd

• describe the parameter passing and scope
• identify the differences between local and global
  variables
• manipulate numbers and text using built in
  subroutines

4
What is a module?

• a.k.a. subprogram, function/procedure, method,
  subroutines
• one, clearly defined purpose
• should be small - less than 20 lines - no more
  than two levels of nesting
• almost always has parameters

5
How important is modularity?

• It is the most important programming/problem
  solving skill in the grade 11 course.
• Students need as much exposure and practice as
  possible.
• Modularity should be incorporated with other
  curriculum expectations wherever possible.

6
Design and use of modules in other expectations

• At the low level
• bottom up
• investigating repetition structures using
  animation
• investigating selection structures by writing
  Boolean functions (a.k.a. predicates)

• At the high level
• top down
• steps of the problem solving model
• planning
• implementation
• testing
• maintenance
• approach each from a modular point of view

7
Progression of modular coding...

• use existing subprograms
• recognize the relationship between actual and
  formal parameters
• write the body of a subprogram given a header

• write a small program given stubs
• design small programs involving subprograms with
  parameters
• design large programs which can be divided among
  several programmers

8
Use existing subprograms ...

• A sample problem using character graphics and
  built-in string subroutines
• Write a subprogram called scroll which will make
  a word scroll across the screen from left to
  right.
• Variations
• Let the user enter the word.
• Pass the word as a parameter to scroll.

9
Develop good habits early.

• as soon as possible, have students write
  subprograms rather than programs
• subprograms with parameters make solutions more
  flexible
• For example
• Write a procedure to calculate the length of a
  hypotenuse of a right angled triangle, given the
  lengths of the other two sides.

10
Parameter passing ...

• actual parameter - used when calling the
  subprogram
• formal parameter - used in the header of the
  subprogram
• parameters may be passed by value or passed by
  reference
• students must be able to follow the flow of
  control

11
What is a stub anyway?

• subprogram header - name, parameter list, return
  type
• internal documentation
• code which outputs the defined purpose of the
  subprogram (usually one line)
• default return type (if necessary)
• should be easily derived from the planning stage
  of the problem solving process

12
Modularity and OO-Design

• objects have attributes and behaviours
• record fields can be analogous to attributes
• subprograms can act as behaviours
• create assignments which model objects
• for example write a program that will simulate a
  digital watch or clock
• time set
• increment time
• display in different formats

13
Assignment ideas

• small
• medium
• large