为什么要先执行count呢，是考虑效率吗？
public class Hello{
public static void main(String[] args){
int num = 10;
int count = 0;
if (num >= 0 && num<=999999999){
while(num != 0){
//count++;
num=num/10;
count++;
}
System.out.println("它是个"+ count+"位的数！");
} else{
System.out.println("输入有误！");
}
}
}
