c - Finding the maximum element of an array recursively

Question

Consider this code, which computes the maximum element of an array.

#include <stdio.h>

int maximum(int arr[], int n)
{
    if (n == 1) {
        return arr[0];
    } else {
        int max = maximum(arr, n-1);
        printf("Largest element : %d
", max);
        return 5; // return arr[n-1] > max ? arr[n-1] : max;
    }
}

int main()
{
    int array[5] = {5, 23, 28, 7, 1};
    printf("Maximum element of the array is: %d", maximum(array, 5));
    return 0;
}

Why is the else block called four (4) times?

Answer 1

The function is recursive, thus it will be called multiple times.

When you first start, n=5. It will take the else block (n is not 1). Then, you call maximum again with n-1 (n=4). Again, the else block is taken.

All told, the function is called 4 times before n reaches 1, whereupon it takes the if block and returns ar[0].

As others have mentioned, the function as written will not return the maximum value of the list. Curiously, it seems to always return 5 unless the list array size is 1, in which case it returns the value of that element.

Instead, a recursive approach would typically involve splitting the list in half each time, then returning the max of each pair when the list finally broken into pairs of elements.