Computer programs can be broken down into smaller sub-programs or subroutines to make the code easier to write, understand and maintain. Sub-programs are independent blocks of code that carry out specific tasks and can be programmed and tested separately from the main program. Functions are sub-programs that return a value, while procedures produce an effect without returning a value. Parameters allow data to be passed from the main program to sub-programs.

1. SUB PROGRAMS
Higher Computing Science

2. MODULAR CODE
• Computer programs are much easier to write and understand if they are
broken down into smaller blocks. These blocks are called sub-programs
or subroutines.
• Large programs will have teams of developers working on them. Using
sub-programs makes it easier to develop and maintain code.

3. SUB-PROGRAMS
• Independent block of code within the main program.
• Carries out a specific task e.g.
• calculate_area
• display_total
• move_player
• update_score
• Can be programmed and tested independently of other sub-programs.

4. SUB-PROGRAMS
• Each sub-program begins with a declaration which includes:
• the sub-program name
• a list of formal parameters being passed into the sub-program

5. FUNCTIONS
• A function is a sub-program which returns a value

6. PROCEDURES
• A procedure is a sub-program which produces an effect

7. PARAMETER PASSING
• Parameters are items of data that can be passed from the main program
to sub-programs.
Main
Program
Sub-program
Parameter

8. PARAMETER PASSING: PSEUDOCODE
FUNCTION calc_rectangle_area(length, breadth)
area = length * breadth
RETURN area
END FUNCTION
area_rect_1 = calc_rectangle_area(10, 4)
display area_rect_1
area_rect_2 = calc_rectangle_area(3, 6)
display area_rect_2

9. PARAMETER PASSING: PYTHON

10. FORMAL PARAMETERS
• Formal parameters are identified in the sub-program definition.
Formal
parameters

11. FORMAL PARAMETERS
• Actual parameters are data items that are passed to the sub-program.
Actual
parameters