Add function

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
typedef struct
{
    char f[100]; // firstname
    char l[100]; // last name
    char n[100]; //number
}contact; //struct name
void main ()
{
    FILE *fp;
    fp = fopen("phonebook.txt","w");
    printf("How many contacts do you want to add: ");
    int n;
    scanf("%d",&n);
    int i;
    contact arr[n];
    for (i=0;i<n;i++)
    {
        printf("Enter firstname: \n");
        scanf("%s", arr[i].f);
        printf("Enter lastname: \n");
        scanf("%s", arr[i].l);
        printf("Enter number: \n");
        scanf("%s", arr[i].n);
    }
    for (i=0;i<n;i++)
    {
        fprintf(fp,"%s",arr[i].f);
        fprintf(fp,",%s",arr[i].l);
        fprintf(fp,",%s.",arr[i].n);
        fprintf(fp,"\n");
    }
    fclose(fp);

}