using System;
using System.Collections.Generic;
using System.Text;

namespace ConsoleApplication1
{
    class Program
    {
        class shape
        {
            public double Area(double x, double y, double z)
            {
                double q;
                q = (x + y + z) / 2;
                return (System.Math.Sqrt(q * (q - x) * (q - y) * (q - z)));
            }
            public double Area(double m, double n)
            {
                return (2.1 * 2.3);
            }
            public double Area(double r)
            {
                return (3.1415 * r * r);
            }
            public double Area(double r, double h)
            {
                return (3.1415 * r * h);
            }
        }
        static void Main(string[] args)
        {

         

        }

    }
}

每个方法前都加static，这样不用实例化类就能调用方法了

静态，怎么做啊？

两个办法。一：给所有要在main()里调用的方法名前加上关键字static，就可以直接调用方法 比如：public static double Area(double x, double y, double z){……}
二：在main()方法里创建一个shape类的对象。然后使用对象名.方法名来调用

我帮你修改一处，然后调用这一处  其他相似


 public static double Area(double r)   //关键字static
            {
                return (3.1415 * r * r);
            }


  private void textBox1_TextChanged(object sender, EventArgs e)
        {
            double q= Convert.ToDouble( textBox1.Text.Trim( ));
            textBox2.Text = shape.Area(q).ToString();
        }

上面的只是简单调用 呵呵  最好加上异常处理 呵呵