Dynamic Array in c using realloc()

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C++

C

Hello Experts,

Good morning.
I am having so trouble to understand why the expeted output is differening from the real output. I am expecting the array to remain the same with ealloc, only adding the new part, but for some reason, the original data is being manipulated. Please take a look at my code, if you have 5 minutes to spare.

Thanks :)

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

int main(void)
{
    int *arr;
    int *data;

    short i = 0;

    arr  = (int*)malloc(10* sizeof(int));
    for(i=0; i<10; i++)
    {
             arr[i]=i;
    }


    for(i=0; i<10; i++)
    {
             printf("\n%d", arr[i]);
    }

     printf("\n\nTESTING!");

     data = (int*)realloc(arr,sizeof(int));
     data[10] = 181;
     arr = data;

     free(data);

    for(i=0; i<12; i++)
    {
             printf("\n%d", arr[i]);
    }

    free(arr);

    scanf("%d", &i);
  return 0;
}