public class HelloWorld{
public static void main(String[] args){
int num = 999;
int count = 0;
do {
count= count + 1;
num = num/10;
}
while(num < 1);
System.out.println("它是个"+count+"位的数");
}
}
while里面的表达式写错了，应该改为while(num>1);
do.....while();循环里面的条件给他限制了