Thread: write input from user in binary file

I'm trying to take input from user and write it into binary file. This is my code, it runs smoothly but when I try to read the file in another (shows that its NULL) so I'm not sure why the data is not being saved into the file.

Code:

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


int length=2, width=2;


struct LandData
{
    int height;
};


struct LandData* WritingData()
{
    FILE *fptr;
    struct LandData *arr = (struct LandData*)malloc(length* width* sizeof(struct LandData));


    if ((fptr = fopen("data.bin","wb")) == NULL){
       printf("Error! opening file");
        exit(1);
    }


    for (int i = 0; i < length ; i++){
        for (int j = 0; j < width; j++){
            printf("choose height: ");
            scanf("%d", &(arr + i*width + j)->height);
            fwrite(arr, sizeof(struct LandData), 1, fptr);
        }
    }


    fclose(fptr);
    return(arr);
}


int main()
{
    struct LandData *arr =WritingData();
    free(arr);
    return 0;
}