1.设计一个学生成绩类，数据成员包括：班级，姓名，英语成绩、c#成绩、数据库；
方法成员包括：有参构造函数（参数为：班级，姓名，英语成绩、c#成绩、数据库），
计算总分，计算平均分，判断等级（平均在85，且各科成绩在75分以上为“优秀”
平均在75，且各科成绩在70分以上为“良好”其它“合格”）
2.采用WinForm形式设计程序，界面根据需要自行设计（考虑输入与输出），所有方法都要使用。

class MyScore
{
    string grade;
    string name;
    double engScore;
    double cSharpScore;
    string database;
    public MyScore(string Grade,string Name,double EngScore,double CSharpScore,string Database)
    {
        this.grade=Grade;
        this.name=Name;
        this.engScore=EngScore;
        this.cSharpScore=CSharpScore;
    `   this.database=Database;
    }
    ····//再接着写一些你说的计算总分方法、平均分方法等
}
构造函数与包含它的类同名，以上的就是有参构造函数。在应用程序主入口函数中实例化一个对象，再调用类里面的方法。

实例化class student=new class()；是这样吗？求继续赐教！

MyScore myscore=new MyScore("二班"，"张三", 89.8, 90.0, 97.5);
上面的具体值对应相应的参数。然后再后面调用你所写的方法，最后就可以输出二班的张三总分多少，平均分多少等等···

你找找资料看看C#类的知识吧。这个算基础了。

{
            string grade = Convert.ToString(textBox1.Text.Trim());
            string name = Convert.ToString(textBox2.Text.Trim());
            double sql = Convert.ToDouble(textBox3.Text.Trim());
            double english = Convert.ToDouble(textBox4.Text.Trim());
            double csharp = Convert.ToDouble(textBox5.Text.Trim());
            student h = new student(  grade,name,sql,english,csharp);
            label6.Text = Convert.ToString(h.zongfen(english, csharp,sql));
           

        }
        class student
        {
            string grade;
            string name;
            double sql;
            double english;
            double csharp,pj;
            public student(string grade, string name, double sql, double english, double csharp)
            {
                this.grade = grade;
                this.name = name;
                this.sql = sql;
                this.english = english;
                this.csharp = csharp;
            }
            public double zongfen(double english, double csharp,double sql)
            {
                return english + csharp+sql ;
            }
            public double average(double english, double csharp,double sql)
            {
                return pj = (english + csharp+sql) / 3;
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            string grade = Convert.ToString(textBox1.Text.Trim());
            string name = Convert.ToString(textBox2.Text.Trim());
            double  sql = Convert.ToDouble(textBox3.Text.Trim());
            double english = Convert.ToDouble(textBox4.Text.Trim());
            double csharp = Convert.ToDouble(textBox5.Text.Trim());
            student h = new student(grade, name, sql, english, csharp);
            label7.Text = Convert.ToString(h.average(english, csharp,sql));
        }
还可以怎么改进？肚子里的墨水太少，初次接触c#，另外判断等级的带码不怎么会写。求赐教！

判断等级可以用if else 加&&
if(平均分>85&&英语分>80&&...)
{console.writeline("优秀");
}
else if(平局分>80&&英语分>80&&...)
{console.writelin("良");
}
else if
。。。

{
            string grade = Convert.ToString(textBox1.Text.Trim());
            string name = Convert.ToString(textBox2.Text.Trim());
            double sql = Convert.ToDouble(textBox3.Text.Trim());
            double english = Convert.ToDouble(textBox4.Text.Trim());
            double csharp = Convert.ToDouble(textBox5.Text.Trim());
            student h = new student(  grade,name,sql,english,csharp);
            label6.Text = Convert.ToString(h.zongfen(english, csharp,sql));
           

        }
        class student
        {
            string grade;
            string name;
            double sql;
            double english;
            double csharp,pj;
            public student(string grade, string name, double sql, double english, double csharp)
            {
                this.grade = grade;
                this.name = name;
                this.sql = sql;
                this.english = english;
                this.csharp = csharp;
            }
            public double zongfen(double english, double csharp,double sql)
            {
                return english + csharp+sql ;
            }
            public double average(double english, double csharp,double sql)
            {
                return pj = (english + csharp+sql) / 3;
            }
            public string dengji(double english, double csharp, double sql)
            {
                if (pj >= 85 && english > 75 && csharp > 75 && sql > 75)
                {
                    return "优秀";
                }
                else if (pj >= 75 && english > 70 && csharp > 70 && sql > 70)
                {
                    return "良好";
                }
                else
                {
                    return "合格";
                }
            }
        }

        private void button2_Click(object sender, EventArgs e)
        {
            string grade = Convert.ToString(textBox1.Text.Trim());
            string name = Convert.ToString(textBox2.Text.Trim());
            double  sql = Convert.ToDouble(textBox3.Text.Trim());
            double english = Convert.ToDouble(textBox4.Text.Trim());
            double csharp = Convert.ToDouble(textBox5.Text.Trim());
            student h = new student(grade, name, sql, english, csharp);
            label7.Text = Convert.ToString(h.average(english, csharp,sql));
        }
      
        private void button3_Click(object sender, EventArgs e)
        {
           string grade = Convert.ToString(textBox1.Text.Trim());
            string name = Convert.ToString(textBox2.Text.Trim());
            double  sql = Convert.ToDouble(textBox3.Text.Trim());
            double english = Convert.ToDouble(textBox4.Text.Trim());
            double csharp = Convert.ToDouble(textBox5.Text.Trim());
            student h = new student(grade, name, sql, english, csharp);
            label8.Text = Convert.ToString(h.dengji(english, csharp,sql));
        }
      
            




    }
}
为什么无论我输入多少分成绩都是显示为合格的？显示不了优秀或良好的，到底哪里出错了？求大神指教！！！感激不尽！！

首先是你的判断语句里pj >= 85 && english > 75 && csharp > 75 && sql > 75中&&的意思是有四个条件都必须为True才返回优秀。
                if (pj >= 85 && english > 75 && csharp > 75 && sql > 75)
                {
                    return "优秀";
                }
                else
                {
                    if (pj >= 75 && english > 70 && csharp > 70 && sql > 70)
                    {
                        return "良好";
                    }
                    else
                        return "合格";
                }

在判断方法里pj不是字段,只是前面的局域变量
if (pj >= 85 && english > 75 && csharp > 75 && sql > 75)
改成下面会不会好使
if (average(double english, double csharp,double sql) >= 85 && english > 75 && csharp > 75 && sql > 75)
仅供参考