应该把分数都定义成double变量更加合理，毕竟分数会有小数的情况存在

public class demo1 {
    public static void main(String[] args) {
        int clanum=4;
        int stunum=3;
        for(int c=1;c<=clanum;c++){
            double sum=0;
            System.out.println("***输入第"+c+"个班级的学生分数***");
            for(int s=1;s<=stunum;s++){
                System.out.print("输入第"+s+"个的学生分数：");
                double score=new Scanner(System.in).nextDouble();
                sum=sum+score;
            }
            double avg=sum/stunum;
            System.out.println("平均分："+avg);
        }
    }
}