public class HelloWorld{
public static void main(String[] args){
int num = 999;
int count = 0;
if(num>0 && num<=999999999){
    for(int i=0;i<10;i++){
    num /= num;
    count++;
    switch(count){
        case 1:
            break;
        case 2:
            break;
        case 3:
            System.out.println("它是个3位的数！");
            break;
        case 4:
            break;
        case 5:
            break;
    }
}
}else{
    System.out.println("请正确输入");
}