Types of Functions in C

Here are some common types of functions in C:

1. Standard Library Functions:

These functions are provided by the C standard library and are available for use in any C program without the need for additional declarations or definitions. Examples include functions like printf, scanf, malloc, free, and strlen

2. User-Defined Functions:

User-defined functions are functions created by the programmer to perform specific tasks. These functions are defined by the programmer and can be customized to suit the program's needs. User-defined functions are further categorized into several types:

a. Function with No Return Value (void functions): These functions do not return a value. They are typically used for performing tasks or operations without producing a result. For example:

c
void printMessage() {
    printf("Hello, World!\n");
}

b. Function with a Return Value: These functions return a value after performing their tasks. The return type is specified in the function declaration. For example:

c
int add(int a, int b) {
    return a + b;
}

c. Function with Parameters: Functions can accept parameters (also known as arguments) that allow you to pass data to them. Parameters are used within the function to perform operations. For example:

c
double calculateArea(double radius) {
    return 3.14159265359 * radius * radius;
}

3. Recursive Functions:

Recursive functions are functions that call themselves either directly or indirectly. They are useful for solving problems that can be broken down into smaller, similar subproblems. A classic example is the factorial calculation:

c
int factorial(int n) {
    if (n == 0) {
        return 1;
    } else {
        return n * factorial(n - 1);
    }
}

4. Library Functions:

These are functions provided by external libraries that are not part of the C standard library. To use library functions, you typically need to include the appropriate header files and link against the library during the compilation process. Examples include functions from math libraries, graphics libraries, and more.

5. Static Functions:

Functions declared with the static keyword have file scope, meaning they are only visible within the source file where they are defined. Static functions are not accessible from other source files, making them useful for encapsulating functionality within a single file:

c
static int fileScopeFunction() {
    // This function is only visible within this source file.
}

6. Inline Functions:

Inline functions are a compiler-specific feature that suggests to the compiler that a function's code should be inserted directly at the call site rather than making a function call. This can improve performance for small, frequently called functions:

c
inline int multiply(int a, int b) {
    return a * b;
}

Different aspects of function calling

A function may or may not accept any argument. It may or may not return any value. Based on these facts, There are four different aspects of function calls.

1. function without arguments and without return value

2. function without arguments and with return value

3. function with arguments and without return value

4.function with arguments and with return value

1.Example for Function without argument and return value:

c
#include <stdio.h>

// Function declaration (prototype)
void printGreeting(void);

int main() {
    // Function call
    printGreeting();

    return 0;
}

// Function definition
void printGreeting(void) {
    printf("Hello, this is a simple C function!\n");
}

Output:

Hello, this is a simple C function!

2.Example for Function without argument and with return value:

c
#include <stdio.h>

// Function declaration (prototype)
int generateRandomNumber(void);

int main() {
    // Function call
    int randomNumber = generateRandomNumber();

    // Display the generated random number
    printf("Random Number: %d\n", randomNumber);

    return 0;
}

// Function definition
int generateRandomNumber(void) {
    // Generate and return a random number (for simplicity, we use 42 here)
    return 42;
}

Output:

Random Number: 42

3.Example for Function with argument and without return value::

c
#include <stdio.h>

// Function declaration (prototype)
void greetUser(char *name);

int main() {
    char userName[] = "John";
    
    // Function call
    greetUser(userName);

    return 0;
}

// Function definition
void greetUser(char *name) {
    printf("Hello, %s! Welcome to the program.\n", name);
}

Output:

Hello, John! Welcome to the program.

4.Example for Function with argument and with return value:

c
#include <stdio.h>

// Function declaration (prototype)
int square(int number);

int main() {
    int num = 5;
    
    // Function call
    int squaredValue = square(num);

    // Display the squared value
    printf("The square of %d is %d\n", num, squaredValue);

    return 0;
}

// Function definition
int square(int number) {
    // Calculate and return the square of the given number
    return number * number;
}

Output:

The square of 5 is 25