C program to write characters in existing file using fputc()

#include<stdio.h>
#include<conio.h>
 void main()
 {char ch;
  FILE *vk=fopen("vvv.txt","wb"); //to write"w" in the file
  clrscr();
  if(vk==NULL)            //if file doesnot exit(NULL), exit from program
   {
    printf("\n\n File does not exit \n");
    exit(0);
    }
    printf("\n\n Enter 0 to exit ");
   while(1)
   {ch=getche();
    if(ch=='0')
     break;
    fputc(ch,vk);
    }
   fclose(vk);
    getch();
    }