c - Reversing n characters of a file -

i trying write small program reverse first n characters of text in file. wrote this::

void getdata(file *fp) {     char ch;     printf("enter text::\n");     while((ch=getchar())!=eof)         fputc(ch,fp); }  void printdata(file *fp) {     char ch;     while((ch=fgetc(fp))!=eof)         putchar(ch); }  void reverse(file *fp, int n) {     char ch[20];     for( int i=0;i<n;++i)         ch[i]=fgetc(fp);     rewind(fp);     printf("%.*s\n",n,ch); //printing string     while(n--)         fputc(ch[n-1],fp); }  int main() {     file *fp;     int n;     fp=fopen("music.txt","w+");     getdata(fp);     rewind(fp);     printf("number of chars reverse:: ");     scanf("%d",&n);     reverse(fp,n);     rewind(fp);     printf("after reversing text is::\n");     printdata(fp);     fclose(fp);     return 0; } 

and output

where going wrong? why there 'u' ? edit: work replacing while loop with

for( int i=0;i<n;++i)         fputc(ch[n-1-i],fp); 

but fault in while?

the fault in while first loop decrement n. in use case n start 4 instead of 5. assign char @ n-1, means n has start 5. @ end loop 4 time long instead of 5.

change

while(n--)         fputc(ch[n-1],fp); 

to

do {    fputc(ch[n-1],fp); }while(--n); 

another little thing. reverse function not checking n passed cannot > of ch length, in case 20.