Function Pointers in C are pointers that point to the address of a function. They are used to call functions indirectly and allow passing functions as arguments to other functions.

Syntax:

return_type (*pointer_name)(parameter_types);

Example:

int (*fptr)(int, int);  // Pointer to a function that returns int and takes two int parameters

Examples:

1. Callback Functions: Used in libraries to pass custom behavior to functions (e.g., sorting algorithms or event handling).

   void callback_function(int val) { /* do something */ }
   void register_callback(void (*callback)(int)) {
       callback(10);  // Calls callback_function
   }
   

2. Dynamic Dispatch: Choosing functions dynamically at runtime, such as state machines or virtual function tables.

   typedef void (*StateFunction)();
   StateFunction state = someFunction;
   state();  // Calls someFunction dynamically
   

3. Plugin Mechanism: Allow swapping functionality without altering the core code.

4. Efficient Code: Reduces code duplication by reusing behavior in different contexts.

Example:

#include <stdio.h>
void add(int a, int b) { printf("Sum: %d\\\\n", a + b); }
void subtract(int a, int b) { printf("Difference: %d\\\\n", a - b); }

int main() {
    void (*operation)(int, int);  // Function pointer
    operation = add;  // Assign function to pointer
    operation(5, 3);  // Call add(5, 3)
    operation = subtract;
    operation(5, 3);  // Call subtract(5, 3)
}