Question

How to replace every element in array by multiplication of next and previous elements with C

Answer 1

// arr[first] = arr[first] (itself) * arr[next];
// arr[last] = prev * arr[last] (itself);

#include <stdio.h>

void MultiplyNextPrevious(int arr[], int size) {
    if (size <= 1)
        return;

    int prev = arr[0];

    arr[0] = arr[0] * arr[1];
    
    for (int i = 1; i < size - 1; i++) {
        int curr = arr[i];

        arr[i] = prev * arr[i + 1]; // arr[i + 1] = next

        prev = curr;
    }

    arr[size - 1] = prev * arr[size - 1];
}

int main()
{
    int arr[] = { 2, 3, 5, 6, 12, 8, 10, 7 };

    int size = sizeof(arr) / sizeof(arr[0]);

    MultiplyNextPrevious(arr, size);

    for (int i = 0; i < size; i++)
        printf("%4d", arr[i]);
}




/*
run:

   6  10  18  60  48 120  56  70

*/

 

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