Question

Improve the sorting example given by writing a choose_direction function that returns a pointer to one of compare_greater and compare_less, depending on whether the user inputs an A or not. The if-then-else construct in the main function can then be replaced by : sort(data,number_of_numbers,choose_direction());.

Answer 1

C CODE:

#include <stdio.h>

#include <stdlib.h>

#define NUMBERS 100

#define TRUE 1

#define FALSE 0

typedef int DataType[NUMBERS];

int CompareGreater(int This,int That) {

    return(This>That);

}

int CompareLess(int This,int That) {

    return(This<That);

}

void Swap(int *This,int *That) {

    int Temporary;

    Temporary = *This;

    *This = *That;

    *That = Temporary;

}

void Sort(DataType Data,int Size,int (*CompareFunction)(int,int)) {

    int Index,SwapOccured;

    SwapOccured = TRUE;

    while (SwapOccured) {

        SwapOccured=FALSE;

        for (Index=0; Index<Size-1; Index++)

            if ((*CompareFunction)(Data[Index],Data[Index+1])) {

                Swap(&Data[Index],&Data[Index+1]);

                SwapOccured = TRUE;

            }

    }

}

int GenerateData(DataType Data) {

    int HowMany,Index;

    printf("How many numbers (max %d) : ",NUMBERS);

    scanf("%d",&HowMany);

    for (Index=0; Index < HowMany; Index++) {

        Data[Index] = rand();

    }

    return(HowMany);

}

void OutputData(DataType Data,int HowMany) {

    int Index;

    printf("The numbers are\n");

    for (Index=0; Index < HowMany; Index++) {

        printf("%d ",Data[Index]);

    }

    printf("\n");

}

char InputDirection(void) {

    char Direction;

    printf("(A)scending or (D)ecending : ");

    scanf(" %c",&Direction);

    return(Direction);

}

// Function which returns a function pointer to a function

// which takes two ints and returns an int

int (*choose_direction(void))(int, int){

    char Direction=InputDirection();

    if (Direction=='A' || Direction=='a')

        return &CompareGreater;

    return &CompareLess;

}

int main(void) {

    DataType Data;

    int NumberOfNumbers;

    char Direction;

    NumberOfNumbers=GenerateData(Data);

    OutputData(Data,NumberOfNumbers);

    

    Sort(Data,NumberOfNumbers,choose_direction());

    

    OutputData(Data,NumberOfNumbers);

    return(EXIT_SUCCESS);

}

SAMPLE OUTPUT:

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