输出百位是3的数,,,填空 初学者请教

#include <iostream.h>
void main()
{
long int num;
cin> > num;
do
{
if(?)
cout < <num < <endl;
cin> > num;
}while(?);
}



[解决办法]
bool IsTree(int input)
{
return ( (input/100)%10 == 3 );
}
---

do
{
if( IsTree(num) )
cout < <num < <endl;
cin> > num;
}while(num != 0);