Function Pointers

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/*$T Fig08_20.cpp GC 1.140 04/10/12 15:37:25 *//* Multipurpose sorting program using function pointers. */#include <iostream>#include <iomanip>using namespace std;/* prototypes */void                        selectionSort(int[], const int, bool(*) (int, int));void                        swap(int *const, int *const);bool                        ascending(int, int);        /* implements ascending order */bool                        descending(int, int);        /* implements descending order *//* =======================================================================================================================  2012.04.10  By KeKe ======================================================================================================================= */void main(){        /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/        const int        arraySize = 10;        int                        order;                /* 1= ascending,2= descending */        int                        counter;        /* array index */        int                        a[arraySize] = { 2, 6, 4, 8, 10, 12, 89, 68, 45, 37 };        /*~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~*/        cout << "Enter 1 to sort in ascending order,\n" << "Enter 2 to sort in descending order: ";        cin >> order;        cout << "\nData items in originalorder\n";        /* output original array */        for(counter = 0; counter < arraySize; ++counter) cout << setw(4) << a[counter];        /*         * sort array in ascending order;         * passfunction ascending ;         * as an argument to specify ascending sorting order         */        if(order == 1)        {                selectionSort(a, arraySize, ascending);                cout << "\nData items in ascending order\n";        }        /* end if */        /*         * sort array in descending order;         * pass function descending ;         * as an argument to specify descending sorting order         */        else        {                selectionSort(a, arraySize, descending);                cout << "\nData items in descending order\n";        }        /* end else part of if...else */        /* output sorted array */        for(counter = 0; counter < arraySize; ++counter) cout << setw(4) << a[counter];        cout << endl;}                /* end main *//* =======================================================================================================================    multipurpose selection sort;    the parameter compare is a pointer to ;    the comparison function that determines the sorting order ======================================================================================================================= */void selectionSort(int work[], const int size, bool (*compare) (int, int)){        int smallestOrLargest;                /* index of smallest (orlargest) element */        /* loop over size -1 elements */        for(int i = 0; i < size - 1; ++i)        {                smallestOrLargest = i;        /* first index of remaining vector */                /* loop to find index of smallest (or largest) element */                for(int index = i + 1; index < size; ++index)                        if(!(*compare) (work[smallestOrLargest], work[index])) smallestOrLargest = index;                swap(&work[smallestOrLargest], &work[i]);        }        /* end if */}                /* end function selectionSort *//* =======================================================================================================================    swap values at memory locations to which ;    element1Ptr and element2Ptr point ======================================================================================================================= */void swap(int *const element1Ptr, int *const element2Ptr){        int hold = *element1Ptr;        *element1Ptr = *element2Ptr;        *element2Ptr = hold;}        /* end function swap *//* =======================================================================================================================    determine whether element a is less than ;    element b for an a scending order sort ======================================================================================================================= */bool ascending(int a, int b){        return a < b;        /* returns true ifa is less than b */}        /* end function ascending *//* =======================================================================================================================    determine whether element a is greater than ;    element b for a descending order sort ======================================================================================================================= */bool descending(int a, int b){        return a > b;        /* returns true if a is greater than b */}        /* end function descending */
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