大神帮忙解释一下这段代码，不知道count怎么来的

int num =1232999;
int count = 0;
if (num >= 0 && num <=999999999){
while(num != 0){
count ++;
num = num/10;
}
System.out.println("它是个" + count + "位的数！");
}else{
    System.out.println("输入有误！");
}
}
}