media aritmetica scrisa in fisier

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

int main()
{
    FILE *f;
    int n,m,j,i,a[20][20],nr=0,max,s=0;
    float media;
    printf("n=");
    scanf("%d",&n);

    for(i=0;i<n;i++)
       for(j=0;j<n;j++){
        printf("a[%d][%d]",i,j);
        scanf("%d",&a[i][j]);

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

    max=a[0][0];
    for(i=0;i<n;i++)
       for(j=0;j<n;j++){
        if(a[i][j]>max){
            max=a[i][j];
            nr=1;

        }else
        if(a[i][j]==max)
            nr++;
       }
       printf("\n%d",nr);
       for(i=0;i<n;i++){
        for(j=0;j<n;j++)
            s=s+a[i][j];
            media=(float)s/(n*n);}
            printf("\n%f",media);
            f=fopen("rezultat.txt","w");
            fprintf(f,"%f" "\n%d",media,nr);

            fclose(f);
    return 0;
}