public class HelloWorld{
public static void main(String[] args){
int num = 999;
int count = 0;
if(num>=0&&num<=999999999){
while(num!=o){
count++;
num/=10;
}
System.out.println("它是个"+count+"位的数!")
}else{
System.out.println("输入有误!");
}
while(num!=o){这里0写成了o
while(num!=0){System.out.println("它是个"+count+"位的数!")这里缺;
System.out.println("它是个"+count+"位的数!");括号是成对出现的,最后缺2个}
注意代码缩进,这样更易阅读
修改后的代码
public class HelloWorld{
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!");
    }
  }
}咩哈哈,我懂喽,谢谢你们
循环条件那里写的不对吧,你写的使o不是零