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Comments on What does the greater than 0 indicate in the case of this statement 'if (compare(A[j], A[j+1]) > 0)' ? Thank you.

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What does the greater than 0 indicate in the case of this statement 'if (compare(A[j], A[j+1]) > 0)' ? Thank you.

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Question: There is a list of integers in an array (3,2,1,5,6,4), sort this list in both ASCENDING & DESCENDING order. Create a sort function.

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

void BubbleSort (int A[], int n, int (*compare)(int, int)){

int i,j,temp;        
    for (i=0; i<n; i++){  
        for(j=0; j<n-1; j++){ 
            if (compare(A[j], A[j+1]) > 0){ //regarding this line of code
                temp = A[j];
                A[j] = A[j+1];
                A[j+1] = temp;
            }
         }
    }
}

int main (){

    int i, A[] = {3,2,1,5,6,4};
    BubbleSort(A,6);     
    for (i=0; i<6; i++){
        printf("%d", A[i]);
    }
}
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Read the code... (1 comment)
Read the code...
elgonzo‭ wrote over 2 years ago · edited over 2 years ago

Clearly, compare is a function pointer and an input parameter for the BubbleSort method. But in your main method, you don't provide a function pointer there: BubbleSort(A,6); What do you think will happen because of that omission?

Furthermore, with regard to your Q "What does the greater than 0 indicate [...]". Clearly, when the return value returned by the compare function (more accurately: the function pointed at by the compare function pointer) is greater than zero, then the body of the if statement will be executed. What does the body of the if statement do? Well, read the code in the body of the if statement...