Unit II: Functions and Program Structure

Course: Programming with C (SEC)
Code: CASEC101

Table of Contents

Defining and Accessing Functions

Functions are the building blocks of a C program, allowing for modularity and code reuse.

Defining Functions: A function definition consists of a return type, a function name, and a set of parameters enclosed in parentheses.
Accessing Functions: Functions are accessed (or called) from other functions like main() to perform their specific task.

Data is transferred to functions through arguments, which must have specified data types.

Argument Data Types: You must explicitly specify the data type (e.g., int, float) for each argument in the function header.
Illustration with Examples: Using functions to solve specific problems, such as finding factorials or processing strings, helps clarify how data moves through a program.

Prototypes provide the compiler with necessary information about a function before it is used.

Function Prototypes: A declaration that tells the compiler the function's name, its return type, and the types of its parameters.
Returning Non-integers: While many functions return integers, C allows functions to return other types like float, double, or char.

Storage classes determine the visibility (scope) and lifetime of variables in C.

Class	Keyword	Scope	Lifetime
Automatic	auto	Inside the block/function.	Function execution duration.
External	extern	Global (across files).	Program execution duration.
Static	static	Inside the block/function.	Program execution duration (value is retained).
Register	register	Inside the block/function.	Function execution duration (stored in CPU register).

Scope rules define where a variable is accessible within the program.

Scope Rules: Local variables are only visible within their defined block, whereas global (external) variables can be seen throughout the file.
Block Structure: C uses curly braces {} to define blocks of code, allowing for nested scopes where variables can be protected or shared.
Header Files: Used to share function prototypes and global definitions across different source files (e.g., stdio.h).

Recursion occurs when a function calls itself to solve a smaller version of the same problem.

Recursive Programs: Useful for problems with a repetitive nature, such as the Tower of Hanoi or generating the Fibonacci sequence.
Base Case: Every recursive function must have a termination condition to prevent infinite calls.

The preprocessor handles directives that begin with # before the actual compilation starts.

Functionality: It handles file inclusion (#include), macro expansion (#define), and conditional compilation.

Exam Tip: Be prepared to write a recursive function for Tower of Hanoi or Fibonacci.
Common Mistake: Forgetting to use the static keyword when a variable needs to retain its value between function calls.
Mnemonic: "E-A-S-R" for Storage Classes: Extern, Auto, Static, Register.

Q: What is a recursive function?
A: It is a function that calls itself to solve a sub-problem.

Q: Why are header files used?
A: To include function prototypes and declarations so that functions defined in other files can be used correctly.