Fuction & Recursion

Function and Recursion

Modular Programming (also called Sub-Program)

• Module in C programming language is implented using function.
• Function is formed through grouping some statements to do a particular job.
• Module is needed when a certain block of statement frequently used by other distict in a program.

Advantages of using modules :

1. Top-down design with sub goal, huge program divided into smaller modules.
2. Can be done by more than one programmer.
3. Easier to debug (easier to pin point errors and easy to follow).
4. Modification can be done without effecting overall codes.
5. Easier to document.

Best practice in module programming :

- High Fan-In

- Low Fan-out

- Self-Contained

Library vs User-Defined Function

Function in C divided in two types : Library fuction and User-defined function.

Library Function is a standard function provided by C compiler. Those function described in the header files.

User-defined fuctions is a sel defined functions.

Function Construction

 return-value-type  function-name( parameter-list )

 {
   statements;

 }

return-value-type : data type of the value returned

if return-value-type is void then the fuction will not return value

if not filled, then default data type will be used

parameter-list : list of value sent from the user

Function Prototype

Function prototype objective : to ensure a function is known by the caller and compiler will validate the parameters

syntax :

   return-value-type fuction-name (parameter-list);

Function prototype can also be written : int maximum (int a, int b);

Identifier Scoping

scope of identifier is reachable.

- Local

Declared in a function.

Scope limited in function.

- Global

Declared outside any function.

Can be re-declared in subprogram.

Reachable from any point in the program.

It is advisable not use global varable for :

- Error rate might increase

- Difficlut in debugging

- All functions in the program can change its value.

Passing Parameter

- By-Value : the value is sent to other module

- By Location/reference : the address is sent to other module

Recrusive Definition

Recrusive is a function call inside a certain function calling itself. For recursive problem.

Recrusive function has two components :

~ Base case : return value(constant) without calling next recrusive call.

~ Reduction step : sequence of input value converging to the base case.

Recrusive

Needs :

~ More memory consumption

~ Takes longer time

Generally, use recrusive solution if :

- Difficult to solve iteralitvely.

- Efficiency using recrusive has been reached.

- Efficiency is less important in comparison with readability.

- Memory efficiency and execution time are not the main concern.