这道题为什么能输出它是几位数，我好晕，求指教
public class HelloWorld{
public static void main(String[] args){
int num = 100;
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！");
}
}
}
