利用輸入ctrl-z按enter來跳出while回圈

//利用輸入ctrl-z按enter來跳出while回圈
#include <iostream>
#include <cstdlib>
using namespace std;
int main()
{
   int lower_case_count=0;//counter
   char ch;
   while(cin >> ch)
   {
   if(ch >='a' && ch <= 'z')
   lower_case_count++;
   }
   cout << "lower case count:" << lower_case_count << endl;
system("PAUSE");
return 0;
}