C - Sorting in dynamic array doesn't work for specific number of values

Question

My task is to create a sorting algorithm for integer values read from a file. The values have to be sorted in an array, as the amount of values is variable, I've used a dynamic array of integers (actually my first time).

Now, the algorithm seems to work fine as it prints all values in the correct order, but only until there are 6 values to sort. In that case, there's no output whatsoever, it seems like even the sorting process isn't successful anymore.

Here's my code:

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

void swap(int *a, int *b){
..
}

int main(){
    int i,anzahl,sorted=0,bla;
    FILE *fp;
    int* feld;

    fp=fopen("file","r");
    if (fp==NULL) return 0;
    else {
        fscanf(fp,"%i",&anzahl);
        feld=(int*)calloc(anzahl,sizeof(int));
        for (i = 0; i <= anzahl; ++i) {
            fscanf(fp,"%i",&bla);
            *(feld+i)=bla;
        }
        fclose(fp);
        while (sorted==0){
            for (i = 0; i < anzahl-1; ++i) {
                if (feld[i]>feld[i+1]) swap(&feld[i],&feld[i+1]);
            }
            for (i = 0; i < anzahl-1; ++i) {
                if (feld[i]<=feld[i+1]) sorted=1;
                else {sorted=0; break;}
            }
        }
        for (i = 0; i <anzahl; ++i) {
            printf("%i ",feld[i]);
        }
    }
    return 0;
}

Please excuse the German variable names and the newbie-style code.

If now the content of my "file" is as follows:

6
1
5
1
99
7
8

the program won't work. If I change the number of values, everything is fine, but as long as the number of values is 6, the program won't work, no matter what values there are.

Answer 1

You are going out of bounds causing undefined behavior here:

for (i = 0; i <= anzahl; ++i)
               ^

This line should be comparing less than not equal or less than .

Also checking calloc() return value is always a good idea.