Find Duplicate in Range 0 and n-1

#include <stdio.h>

int find_duplicate(int arr[], int n) {
    // Your logic here
    for(int i=0;i<n;i++){
        int ind=arr[i];
        if(arr[i]<0){
            ind=-1*arr[i];
        }
        if(arr[ind]<0){
            return ind;
        }
        arr[ind]=-arr[ind];
    }
    return -1;
}

int main() {
    int n;
    scanf("%d", &n);

    int arr[100];
    for (int i = 0; i < n; i++) scanf("%d", &arr[i]);

    int result = find_duplicate(arr, n);
    printf("%d", resulct);
    return 0;
}