Easy Notes on PROGRAMMING IN ‘C’ unit-4 @Computer Diploma

Description

4.1 Concept and Need of Functions

• Keywords: C functions, what is a function in C, why use functions, advantages of functions, function definition, function declaration, modular programming, code reusability.
• Description: A function in C is a self-contained block of code designed to perform a specific task. They are fundamental for creating modular, reusable, and organized programs. By using functions, you can break down a large program into smaller, manageable chunks, which simplifies development, debugging, and maintenance. This approach also promotes code reusability, as a function can be called multiple times from different parts of a program, eliminating the need to write the same code over and over again.

4.2 Library Functions

• Keywords: C library functions, predefined functions in C, math.h functions, string.h functions, getchar(), putchar(), malloc(), calloc().
• Description: Library functions are built-in functions provided by the C standard library. You can use them by including the appropriate header files (e.g., <math.h>, <string.h>).
  • Math Functions: The <math.h> header file contains functions for common mathematical operations. Keywords include sqrt(), pow(), sin(), cos(), log(), etc.
  • String Handling Functions: The <string.h> header file offers functions for manipulating strings (character arrays). Keywords include strlen() (string length), strcpy() (copy string), strcat() (concatenate strings), and strcmp() (compare strings).
  • Other Functions:
    • getchar() and putchar(): These are basic I/O functions. getchar() reads a single character from the standard input (keyboard), and putchar() writes a single character to the standard output (screen).
    • malloc() and calloc(): These are dynamic memory allocation functions from <stdlib.h>. malloc() (memory allocation) allocates a block of uninitialized memory. calloc() (contiguous allocation) allocates a block of memory for an array and initializes all bytes to zero. calloc() is slower but safer for arrays as it prevents garbage values.

4.3 Writing User-Defined Functions

• Keywords: User-defined functions in C, C function prototype, function definition, function call, local variables, global variables, scope of variables.
• Description: User-defined functions are functions created by the programmer to perform specific tasks. The process involves three key steps:
  1. Function Declaration (Prototype): This tells the compiler about the function’s name, return type, and parameters. It acts as a signature.
  2. Function Definition: This contains the actual code or logic that the function executes.
  3. Function Call: This is how you invoke or execute a function from another part of the program, such as the main() function.

  The scope of variables is crucial:

  • Local variables are declared inside a function and are only accessible within that function.
  • Global variables are declared outside all functions and are accessible throughout the entire program.

4.4 Function Parameters and Return Values

• Keywords: C function parameters, passing arguments to function, call by value vs call by reference, C function return value, return statement, C function return types.
• Description:
  • Parameter Passing: There are two main ways to pass arguments to a function:
    • Call by Value: A copy of the argument’s value is passed to the function. Changes made to the parameter inside the function do not affect the original variable. This is the default method for simple variables.
    • Call by Reference: The memory address (a pointer) of the argument is passed. This allows the function to directly access and modify the original variable. This is essential when you need a function to change the value of a variable outside its scope.
  • Return Values: A function can return a single value to the calling code using the return statement. The function return type specifies the data type of the value that will be returned. A function with a void return type does not return any value.

4.5 Recursive Functions

• Keywords: C recursion, recursive function, recursion in C, base case, factorial using recursion, Fibonacci series using recursion.
• Description: A recursive function is a function that calls itself, either directly or indirectly, to solve a problem. It works by breaking down a large problem into smaller, identical sub-problems until it reaches a base case, which is a condition that stops the recursion and prevents an infinite loop. While elegant, recursion can be less efficient than iterative solutions due to the overhead of function calls. Common examples include calculating the factorial of a number and generating the Fibonacci sequence.