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();
}

Format Specifiers in C

Let us take a look at some format specifiers used in printf which are necessary to format the output.....

%x--> prints an int in hexadecimal.
%4x--> prints a hex int, right-justified to 4 places. If it's less than 4 digits, it's preceded by spaces. If it's more than 4 digits, you get the full number.
%04x--> prints a hex int, right-justified to 4 places. If it's less than 4 digits, it's preceded by zeroes. If it's more than 4 digits, you get the full number, but no leading zeroes.

example:
void main()
{
int i=98;
printf("%x\n",i);
printf("%4x\n",i);
printf("%04x",i);
getch();
}

output:
62
       62
00062

Similary with %d
void main()
{
int i=5;
printf("%d\n",i);
printf("%4d\n",i);
printf("%04d",i);
getch();
}

output:
5
         5
00005

Similary with %c..
 void main()
{
char c='a';
printf("%c\n",c);
printf("%4c\n",c);
printf("%04c",c);
getch();
}


output:
a
         a

0000a