1. Designing Functions CSIS 1595: Fundamentals of Programming and Problem Solving 1

2. Modular Programming Breaking complex program down into simple functions – Easier to implement, test, and understand Tools: – Major steps in pseudocode used to design program Each major step  separate function – Knowledge of typical functions programs often use Gathering and validating input Computing a complex value using conditions/loops Printing complex/formatted output …

3. Example: Balloon program Pseudocode: 1.Randomly generate and print the target distance 2.Prompt user for a velocity greater than 0 3.Prompt user for an angle in degrees and convert to radians 4.Compute distance balloon misses the target by 5.Determine whether the balloon hits and print the result

4. Function Design Functions in balloon program: – set_target() Generates random target distance, prints and returns it – get_velocity() Prompts for velocity until value > 0 entered, returning it – get_angle() Prompts for angle in degrees and converts to radians – compute_miss(target,velocity,angle) Computes the distance ballon flies and how much it misses the target by – print_result(miss_distance) Determines whether balloon hits and prints result

5. Function Design Common use: Computation to create single value – Limitation: Function can only return one value (more later)

6. Functions with No Arguments Many functions take no arguments – Common use: Getting input from user Syntax: def functionname(): – Still need to include () in the definition

7. Functions with No Return Value Function can return no value – Common use: Printing arguments in some complex way Syntax in function: – No return statement at all or just return with no expression Syntax of calling: functionname(arguments) – No return value to use in assignment

8. Structure of Main Program Often just consists mostly of function calls – Goal: Make main program very simple

9. Functions Calling Functions Functions can contain calls to other functions

10. Hierarchical Design Break program down into main tasks – These will be functions called from main program Break each main task down into subtasks – These will be “subfunctions” called from those functions … Continue until subtasks simple enough for functions

11. Hierarchical Design Example: Balloon table program Pseudocode: 1.Compute and print target distance 2.Prompt user for a velocity greater than 0 3.Loop angle from 0 to 45 every 3 degrees 1.Compute distance balloon misses target by 2.Print angle and result in column format Called by main program Called by loop function

12. Hierarchical Balloon Program