1. Libraries of Code
Notes from Wilson, Software Design and Development Preliminary Course pp

2. What is a Library of Code?
A set of routines or modules stored for future use
Module should work independently
Module should contain
Local variables
Identifiers
Assignment statements that assign values to variables used only within that module

3. Why have a Library of Code
Can copy from Library into a program
If truly independent will need little or no modification
Will reduce time needed to code a program
Will reduce time needed to test the program (because the library code should already have been tested)

4. Reusable Code Reusable code are standard routines
Reusable code often is used to
Data validation
Checking format of data entered is valid for e.g. checking the user entered a valid date
Date conversion
Put date entered into format you need for your code. For e.g. 25th August >
Converting words to numbers
Once coded and tested reusable code can be stored in a library and reused in many programs

5. Using Libraries of Code
Copy and Paste
Calling Modules
As a subprogram
The main program calls the module, follows the module’s instructions, then returns control to main program
As a function
Works similar to a subprogram, but always returns a value to the main program code
Subprograms and functions are often passed variables from the main program

6. Sharing Variables between Main Program and Modules
Variables can be defined as Global or Local
GLOBAL variables can be seen from anywhere in the main program or modules
LOCAL variables are used within modules and cannot be recognised by the main program or other modules

7. Pseudocode Example of main program and modules
begin
declare
globalvariable1 as number
globalvariable2 as date
localvariable1 as number
localvariable2 as date
localvariable3 as number
do subprogram1
localvariable3 = function1(localvariable1,localvariable2)
subprogram1
statement1
statement2
statement3
end
function1 (localvariable 4 as number, localvariable 5 as date)
localvariable6 as number
localvariable4 = localvariable6
Example subprogram, follows steps passes no variable
Example function, follows steps does pass variable