求大神帮忙解答问题，C#编程画圆，出现下列问题，怎么破？

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            class hanshu
            {
                public double F(int x)
                {
                    const double a1=30.58;
                    const double b1=-110.7;
                    const double c1=27.96;
                    double f=a1*Math.Exp(-((x-b1)/c1)*((x-b1)/c1));
                }
            }
           
                    

        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {
           
           
  
           
        }

        private void textBox2_TextChanged(object sender, EventArgs e)
        {
           
        
        }

        private void textBox3_TextChanged(object sender, EventArgs e)
        {
           
        }

        private void button1_Click(object sender, EventArgs e)
        {
             hanshu qiangdu1=new hanshu();
             int x=Convert.ToInt32(textBox1.Text);
             double r1=qiangdu1.F(x);


             hanshu qiangdu2=new hanshu();
             int m=Convert.ToInt32(textBox2.Text);
             double r2=qiangdu1.F(m);


             hanshu qiangdu3=new hanshu();
             int n=Convert.ToInt32(textBox3.Text);
             double r3=qiangdu1.F(n);
     
            
            
            
            Graphics gra = this.pictureBox1.CreateGraphics();
            Pen pen = new Pen(Color.Pink);
            gra.DrawEllipse(pen, 10, 10, Convert.ToInt32(r1), Convert.ToInt32(r1));
            gra.DrawEllipse(pen, 20, 10,Convert.ToInt32(r2), Convert.ToInt32(r2));
            gra.DrawEllipse(pen, 10, 20,Convert.ToInt32(r3), Convert.ToInt32(r3));

        }
    }
}

错误    应输入 class、delegate、enum、interface 或 struct
错误    应输入类型、命名空间定义或文件尾   
错误    “WindowsFormsApplication1.Form1.hanshu.F(int)”: 并非所有的代码路径都返回值