C cannot get search number in array inside while loop to work and "double free or corruption" error

i'm noob in C programming and I'm sorry for this question which could be very easy, but i cannot solve this problem after searching all the afternoon. I'm trying to write a program that generates a random number, checking that this is not already present in a list contained in the file number.txt. At the end the program has to ask if you want to extract another number and, if Yes, re-run it. I tried various for and while loops but none of these worked: numbers in the list are often extracted, What's wrong?

Moreover, sometimes, after various iterations, the program stops with the error "double free or corruption (! prev)", what causes it?

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
#define rangeMAX 27 //Upper limit of range.
#define rangeMIN 1  //Lower limit of range.


int main()
{
  int get, i, n;
  int num[5];
  char r;
  FILE *filer;
    filer = fopen("numbers.txt", "r");
    printf("When you are ready press any key to continue\n");
    getchar();
    if (filer == NULL)
    {
        printf("ERROR Creating File!");
        exit(1);
    }
    do {
        num[5] = 0;
        n = 0;
        i = 0;
        free(filer);
        get = 0;
        r = 0;
            srand(time(0)); // this will ensure that every time, program will generate different set of numbers. If you remove this, same set of numbers will generated every time you run the program.
            get = ((rand() % (rangeMAX-rangeMIN+1)) + rangeMIN); // generate random number.
        for (n = 0; n < 5; n++){
        fscanf(filer, "%d\n", &num[n]);
        }
            for (n = 0; n < 5; n++){
                if (get == num[n]){
                printf("false\n");
                printf("%d\n", n);
                break;
                }
            }
                i=get;
                printf("%d\n",i);
    printf ("Do you want another number? Y/N ");
    scanf (" %c", &r);
    } while (r == 'y' || r == 'Y');
    return(0);

}