Function Pointers in C

FunctionPointers.c

#include <stdio.h>

/* Typical Arithmetic Operations */
int add(int a, int b)
{
    return a + b;
}
int sub(int a, int b)
{
    return a - b;
}
int mult(int a, int b)
{
    return a * b;
}
int divide(int a, int b)
{
    return a / b;
}
// ****************************************
// Typical function pointer

// It has not been typedef'ed
// subtract is the variable name
// you pass it two ints
// it returns an int.

// To assign it, I just give it the name

int (*subtract)(int, int) = sub;

// ********************************************
 // functionpointer typedef
 
 // it defines a function which takes in (int, int) as parameters
 // and returns an int.
 // arith is the name of the type you created.
 
typedef int (*arith)(int, int) ;

// Declaring something with the typedef:
arith adder = add;

/* Passing in a function pointer to a method.
 * This also returns variables through reference.
 */
void doOperationWithNumbers(int a, int b, int *answer, int (*operation)(int, int))
{
    *answer = operation(a, b);
}
/* Or we can use our typedef instead of declaring the whole
 * function pointer again
 */
void otherWayToDoOperation(int a, int b, int *answer, arith operation)
{
    *answer = operation(a, b);
}

int main( int argc, const char* argv[] )
{
    int x = 5, y = 4;
    int ans;
    arith operations[4]; // create space for the operations
    operations[0] = add; // Assign the function by name.
    operations[1] = sub;
    operations[2] = mult;
    operations[3] = divide;
    
    // executing a function pointer:
    subtract(x, y);
    adder(x, y);
    
    
    for (int i = 0; i < 4; i++)
    {
        // Notice the last parameter is an execution
        // of the function pointer.
        
        printf("Operation %d: %d\n", i, operations[i](x, y));
    }
    
    
}