replace file erro

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

void tambahIsi();
void tampilkanIsi();
void replaceIsi();
void hapus();

FILE *f;
int fileHandle;
long int ukuranFile;
int i;

typedef struct{
    char nama[100];
    char alamat[10];
} biodata;

biodata b;

void tambahIsi(){
    f = fopen("textPercobaan.txt","a");
    if(f == NULL){
        printf("File tidak bisa diproses!");
        exit(1);
    }
    i = 0;
    printf("Masukkan nama anda: "); fflush(stdin); gets(b.nama);
    printf("Masukkan alamat: "); fflush(stdin); gets(b.alamat);
    fwrite(&b, sizeof(b),1,f);
    fclose(f);
}

void tampilkanIsi(){
    f = fopen("textPercobaan.txt","r");
    if(f == NULL){
        printf("File tidak bisa diproses!");
        exit(1);
    }
    i = 1;
    fileHandle = fileno(f);
    ukuranFile = filelength(fileHandle);
    if(ukuranFile == -1L){
        printf("Tidak bisa mendapatkan ukuran file");
        fclose(f);
        exit(1);
    }else if(ukuranFile == 0){
        printf("File masih kosong");
        tambahIsi();
    }else{
        printf("====== Tampilkan Semua Data ======\n");
        for(;;){
            fread(&b,sizeof(b),1,f);
            if(feof(f)) break;
            printf("%i. Nama: %s\n",i,b.nama);
            printf("    Alamat: %s\n",b.alamat);
            i++;
        }
        fclose(f);
        printf("===================================\n");
    }
}

void replaceIsi(){
    char namaBaru[30];
    char alamatBaru[30];
    int found;
    char cari[20];

    f = fopen("textPercobaan.txt","r+");
    if(f == NULL){
        printf("File tidak bisa diproses!");
        exit(1);
    }


    printf("Masukkan nama yang ingin direplace: "); fflush(stdin); gets(cari);

    found = 0;
    while((fread(&b,sizeof(b),1,f)) > 0 && found == 0){
        if(strcmp(cari,b.nama)==0){
            printf("Nama baru: "); fflush(stdin); gets(b.nama);
            printf("Alamat baru: "); fflush(stdin); gets(b.alamat);
            fseek(f,-(long)sizeof(b),1);
            fwrite(&b, sizeof(b),1,f);
        }
    }

    fclose(f);



}

void hapus(){
    FILE *f2;
    char del[20];
    printf("Masukan nama yang ingin dihapus : "); fflush(stdin);gets(del);

    f = fopen("textPercobaan.txt","r");
    f2 = fopen("temp.txt","w");
    rewind(f);

    while(fread(&b,sizeof(b),1,f) > 0){
       if(strcmp(del,b.nama)!=0){
            fwrite(&b,sizeof(b),1,f2);
            printf("berhasil");
       }else if(strcmp(del,b.nama)==0){
           printf("salah");
       }
    }

    fclose(f2);
    fclose(f);
    remove("textPercobaan.txt");
    rename("temp.txt","textPercobaan.txt");

}

int main(){
    char pilihMenuUtama;


    while(pilihMenuUtama != '5'){
        printf("Menu Utama\n");
        printf("1. tampilkan isi file\n");
        printf("2. tambahkan isi file\n");
        printf("3. replace isi\n");
        printf("4. bersihkan layar\n");
        printf("5. keluar\n");
        printf("6. Hapus\n");
        printf("Pilihan anda: "); pilihMenuUtama = getche();
        printf("\n\n\n");
        switch(pilihMenuUtama){
            case '1':{
                tampilkanIsi();
                break;
            }
            case '2':{
                tambahIsi();
                break;
            }
            case '3':{
                replaceIsi();
                break;
            }
            case '4':{
                system("cls");
                break;
            }
            case '6':{
                hapus();
                break;
            }
        }
    }
    exit(0);
    return 0;
}