有关C++

#include <iostream.h>
void main()
{ float x;
char ch;
cin>>x;
switch(x\10)
{
case 10:
case 9:    ch='A';break;
case 8:    ch='B';break;
case 7:    ch='C';break;
case 6:    ch='D';break;
default:   ch='E';
}
cout<<ch<<endl;
}