public class helloworld{  public static void main(String[] args){   int one=10;   int two=20;   int three=0;  int three = one + two;  int three+= one;  int three-= one;  int three*= one;  int three/= one;  int three%= one; 我这个菜鸟前面写成这样，结果老是出错，我想知道为什么不能这样写？