//------------------------------------------------------------------------------------
// 1.2 Introductory Example or How to Replace a Switch-Statement
// Task: Perform one of the four basic arithmetic operations specified by the
//       characters '+', '-', '*' or '/'.


// The four arithmetic operations ... one of these functions is selected
// at runtime with a swicth or a function pointer
float Plus    (float a, float b) { return a+b; }
float Minus   (float a, float b) { return a-b; }
float Multiply(float a, float b) { return a*b; }
float Divide  (float a, float b) { return a/b; }


// Solution with a switch-statement - <opCode> specifies which operation to execute
void Switch(float a, float b, char opCode)
{
   float result;

   // execute operation
   switch(opCode)
   {
      case '+' : result = Plus     (a, b); break;
      case '-' : result = Minus    (a, b); break;
      case '*' : result = Multiply (a, b); break;
      case '/' : result = Divide   (a, b); break;
   }

   cout << "Switch: 2+5=" << result << endl;         // display result
}


// Solution with a function pointer - <pt2Func> is a function pointer and points to
// a function which takes two floats and returns a float. The function pointer
// "specifies" which operation shall be executed.
void Switch_With_Function_Pointer(float a, float b, float (*pt2Func)(float, float))
{
   float result = pt2Func(a, b);    // call using function pointer

   cout << "Switch replaced by function pointer: 2-5=";  // display result
   cout << result << endl;
}


// Execute example code
void Replace_A_Switch()
{
   cout << endl << "Executing function 'Replace_A_Switch'" << endl;

   Switch(2, 5, /* '+' specifies function 'Plus' to be executed */ '+');
   Switch_With_Function_Pointer(2, 5, /* pointer to function 'Minus' */ &Minus);
}

#include <stdio.h>

int dummy () { return 42; }

typedef int (*fun_ptr)();

int main () {

        int x, y = dummy ();
        fun_ptr call = &dummy;
        x = call ();

        printf ("x : y  -> %d : %d\n", x, y);
        return 0;
}

#include <stdio.h>
#include <stdlib.h>

void printarray(int *, int );

/* 
 * The following says that compar1 is a function that returns
 * an int. It has two parameters, which are void pointers
 */
int (compar1)(const void *, const void *);

/* 
 * The following says that compar2 is a function that returns
 * an int. It has two parameters, which are void pointers
 */
int (compar2)(const void *, const void *);

/* 
 * The fourth parameter to qsort is a pointer to a function.
 * The function has two parameters which are void pointers, 
 * and the function returns an int.
 *
 * When you use a function name by itself (no parentheses)
 * it is taken to be a pointer whose value is the address of
 * the function.
 *
 * When we call qsort with compar1 it sorts in ascending order.
 * When we call qsort with compar2 it sorts in descending order.
 */

int main()
{
    int x[5] = {3,1,4,2,5};

    printf("Initial array elements  : ");
    printarray(x, 5);

    qsort(x, 5, sizeof(int), compar1);
    printf("After qsort with compar1: ");
    printarray(x, 5);

    qsort(x, 5, sizeof(int), compar2);
    printf("After qsort with compar2: ");
    printarray(x, 5);

    return 0;
}

void printarray(int *x, int siz)
{
    int i;
    for (i = 0; i < siz; i++) {
        printf("%3d ", x[i]);
    }
    printf("\n");
}

/* 
 * compar1 returns a negative value if the first
 * item is less than the second.
 *
 * It returns a positive value if the second is
 * smaller.
 *
 * It returns zero if the two are equal.
 */
int compar1(const void *p1, const void *p2)
{
    const int * ip1 = p1;
    const int * ip2 = p2;
    return (*ip1 - *ip2);
}

/* 
 * compar2 returns a negative value if the second
 * item is first than the second.
 *
 * It returns a positive value if the first is
 * smaller.
 *
 * It returns zero if the two are equal.
 */
int compar2(const void *p1, const void *p2)
{
    const int * ip1 = p1;
    const int * ip2 = p2;
    return (*ip2 - *ip1);
}

#include <stdio.h>
#include <stdlib.h>

void printarray(int *, int );
int (compar1)(const void *, const void *);
int (compar2)(const void *, const void *);

int main()
{
    /* fpointer is an array of two pointers to functions
     * Each the functions has an int return type, and
     * has two parameters, which are void pointers
     *
     * The pointer array is initialized with the addresses
     * of the comparison functions for qsort
     */

    int (*fpointer[2])(const void *,const void *) = {
        compar1,
        compar2 
    };
    int x[5] = {3,1,4,2,5};
    int choice;
    printf("Here's the array:\n");
    printarray(x, 5);
    printf("\n");

    printf("Here are the choices:\n");
    printf("  1. Sort in ascending order\n");
    printf("  2. Sort in descendng order\n\n");
    printf("Enter your selection: ");
    if ((scanf("%d", &choice) != 1) || (choice < 1) || (choice > 2)) {
        printf("Invalid.\n");
        return 0;
    }
    qsort(x, 5, sizeof(int), fpointer[choice-1]);
    printf("OK! Here's the result for selection %d:\n", choice);
    printarray(x, 5);

    return 0;
}

void printarray(int *x, int siz)
{
    int i;
    for (i = 0; i < siz; i++) {
        printf("%3d ", x[i]);
    }
    printf("\n");
}

int compar1(const void *p1, const void *p2)
{
    const int * ip1 = p1;
    const int * ip2 = p2;
    return (*ip1 - *ip2);
}

int compar2(const void *p1, const void *p2)
{
    const int * ip1 = p1;
    const int * ip2 = p2;
    return (*ip2 - *ip1);
}