public class Pratice{
public static void main(String[] args){
int num = 999;
int count = 0;
if(num>=0&&num<=999999999){
 for(;num!=0;){
     count++;
     num=num/10;
 }
System.out.println("它是个" + count + "位的数！");
}
else {
    System.out.println("number is invalid");
}
}
}

public class Practice{
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！");
}

}

}