将文本文件fin.dat中的数字字符找出并写入文本文件fnum.dat中。
#include
void main ()
{
   char ch;
   FILE *fin, *fnum;
   fin=fopen ("fin.dat", __________);   /*第一空*/
   fnum=fopen ("fnum.dat", "w");
   while(!feof(__________))   /*第二空*/
   {
         ch=fgetc(fin);
         if(__________)fputc (ch, fnum);   /*第三空*/
   }
   fclose (fin);
   fclose(fnum);
}