运行成功，输出错误，这是什么意思，代码没错呀
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！");
}
}
}
