public class HelloWorld{
public static void main(String[] args){
int num = 999;
int count = 0;
if(num>=0&&num<=999999999){
    while(num!=0){
        count++;
        num/=10;
         }
    System.out.println("它是个"+count+"位的数！");
        }else{
    System.out.println("输入有误");
        }
    }
}

num/=10;在这组代码中起什么作用？？？？？？？？