Why is my code producing a segmentation fault? - c

Question

So im working on this program that is supposed to take the pointer to an array and the array’s size (number of elements in the array)
as arguments, finds the place the index of the outlier, fixes the array in place (that is puts the outlier to a
place it is supposed to be), and returns the old index where the outlier was found. i finished my code but for some reason, somewhere in my main function its telling me there is a segmentation fault, i know its in my main function because it compiled and ran fine when it was just the original code. heres the code;
#include <stdio.h>
long long int fix_sorted_array(double* arr, unsigned long n)
{
double temp;
int i, j;
for ( i = 0; i < n - 1; i ++)
{
if (arr[i] > arr[i + 1])
{
for ( j = i + 1; j > 0; j --)
{
if (arr[j] < arr[j-1])
{
temp = arr[j];
arr[j] = arr[j-1];
arr[j-1] = temp;
}
}
return i + 1;
}
}
return -1;
}
int main()
{
int n;
int j;//declared variables
double arr[n];
printf("Enter elements of array : \n");
for ( int i = 0; i < n; i ++)
{
scanf("%lf", &arr[i]);
}
printf("Return index : %lld\n",fix_sorted_array (&arr[n], n));
printf("Array after : \n");
for ( j = 0; j < n; j ++)
{
printf("%.2lf", arr[j]);
}
}

Answer 1

You're passing an address outside the array to the function in this line:
printf("Return index : %lld\n",fix_sorted_array (&arr[n], n));
You want to pass the address of the start of the array, not the end, so it should be:
printf("Return index : %lld\n",fix_sorted_array (arr, n));
You also need to initialize n before you declare the array.
printf("How many numbers? ");
scanf("%d", &n);
double arr[n];

Answer 2

You have never accepted the value of n. Below code might help.
#include <stdio.h>
long long int fix_sorted_array(double* arr, unsigned long n)
{
double temp;
int i, j;
for ( i = 0; i < n - 1; i ++)
{
if (arr[i] > arr[i + 1])
{
for ( j = i + 1; j > 0; j --)
{
if (arr[j] < arr[j-1])
{
temp = arr[j];
arr[j] = arr[j-1];
arr[j-1] = temp;
}
}
return i + 1;
}
}
return -1;
}
int main()
{
int n;
int j;//declared variables
printf("Enter the number of elements in arrays");
scanf("%d",&n); // initialize the values of n
double arr[n];
printf("Enter elements of array : \n");
for ( int i = 0; i < n; i ++)
{
scanf("%lf", &arr[i]);
}
printf("Return index : %lld\n",fix_sorted_array (&arr[0], n)); // Also pass the value of starting index in array i.e. `arr[0]`
printf("Array after : \n");
for ( j = 0; j < n; j ++)
{
printf("%.2lf", arr[j]);
}
}