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

}
}