C file handling program to replace the specified line in an existing text file and print the modified content file

\* C file handling program to replace the specified line in an existing text file and print the modified content file *\

# include < stdio.h >
# include < stdlib.h >
# include < string.h >
int   main( )
{

FILE* fp1 ;
FILE* fp2 ;
char ch, filename[20] ;
int line = 0 ;
int temp = 1 ;
int flag = 0 ;

printf("\n Enter the source filename : ") ;
scanf("%s", filename) ;
fp1 = fopen(filename, "r") ;
if (fp1 == NULL)
{
      printf("\n Unable to open file\n") ;
      return -1 ;
}

while (!feof(fp1))
{
      ch = getc(fp1) ;
      printf("%c", ch) ;
}
rewind(fp1) ;

char newText[32] = "\nMy New Line to be added" ;
printf("\n\n Enter line number to replace the line: ") ;
scanf("%d", &line) ;
fflush(stdout) ;
fp2 = fopen("temp.txt", "w") ;

while (!feof(fp1))
{
      ch = getc(fp1) ;
      if (ch == '\n')
            temp++;

      if (temp != line)
      {
            putc(ch, fp2 ) ;
      }

      if (flag == 0 && temp == line)
      {
            fwrite(newText, 1, strlen(newText), fp2) ;
            flag = 1 ;
      }
}

fclose(fp1) ;
fclose(fp2) ;
remove(filename) ;
rename("temp.txt", filename) ;
printf("\nModified file:\n") ;

fp1 = fopen(filename, "r");
if (fp1 == NULL)
{
      printf("\nUnable to open file\n") ;
      return -1 ;
}
while (!feof(fp1))
{
      ch = getc(fp1) ;
      printf("%c", ch) ;
}
fclose(fp1) ;
printf("\n") ;
return 0 ;

}