Comparing Username Stored in File in C

I got a request to read the username from file and compare the same .
Here is the code for the same :

#include<stdio.h>
#include<conio.h>
void main()
{
char ch;
char user_name[128];
char line[128];
char str[128];
char *ptr;
int i=0;
FILE *fp;

//Saving username in file
printf("Enter the username to write in a file:");
ch=getch();
while(ch!=13)
{
if(ch==8)
{
printf("\b");
putch(NULL);
printf("\b");
user_name[i]='\0';
--i;
}
else
{
printf("%c",ch);
user_name[i++]=ch;
}
ch=getch();
}
user_name[i]='\0';
ptr=user_name;
fp=fopen("d:\\user.txt","w+");
while(*ptr!='\0')
{
fputc(*ptr,fp);
ptr++;
}
printf("\nUsername successfully saved in the file");

//Reading username from file and saving to string .
fseek( fp, 0, SEEK_SET );
while(fgets(line,sizeof(line),fp)!=NULL)
   {
   char *nwln=strchr(line,'\n');
   if(nwln!=NULL)
   *nwln='\0';
   }
printf("\nUsername in file is :%s",line);
fp=NULL;

//take username from user to compare.
printf("\nEnter username to confirm:");
fgets(str,sizeof(str),stdin);
str[strlen(str)-1] = '\0';
if(!strcmp(line,str))
{
    printf("\nyou are right");
}
else
{
    printf("\nyou are wrong");
}

getch();
}