3-3 Product

#include <stdio.h>
#include <ctype.h>
int main()
{
 char ch;
 int iNumber=0;
 long lProduct=1;
 
 while((ch=getchar())!=EOF)    //Using getchar()
 {
  if(isdigit(ch))         //Judge whether the char get from console is digit 
  {
   iNumber=iNumber*10+ch-'0';
  }
  else if(' '==ch||'\n'==ch)    //If the char is not digit,then judge whether it is Space or Enter
  {
   lProduct*=iNumber;
   iNumber=0;        //Let iNumber=0,for the next calculation
  }
  else            //If the char is not digt or Space or Enter,it must be other characters like letter,so let iNumber=1,
  {             //because when we input other characters like letter,then iNumber will become 0,
   iNumber=1;        //and everything will become 0.
  }
 }
 printf("%ld\n",lProduct%1000);
}