private void button1_Click(object sender, EventArgs e)
        {
           double r,l,s,v;  //这里说是有错误,无效的表达式,意外的字符,应输入;
            r=Convert.ToDouble(textBox1.Text);
            l=2*Math.PI*r;
            s=Math.PI*r*r;
            v=4.0*Math.PI*r*r*r/3;
            textBox2.Text=Convert.ToSingle(l);
            textBox3.Text=Convert.ToSingle(s);
            textBox4.Text=Convert.ToSingle(v);
        }

private void button1_Click(object sender, EventArgs e)
        {
           double r,l,s,v;
            r=Convert.ToSingle(textBox1.Text);
            l=2*Math.PI*r;
            s=Math.PI*r*r;
            v=4.0*Math.PI*r*r*r/3.0;
            textBox2.Text=Convert.ToString(l);
            textBox3.Text=Convert.ToString(s);
            textBox4.Text=Convert.ToString(v);
        }

感觉的定义有乱 有写没有必要啊
private void button1_Click(object sender, EventArgs e)
        {
           double r,l,s,v;
            r=double.Parse(textbox1.text);
            l=2*Math.PI*r;
            s=Math.PI*r*r;
            v=4.0*Math.PI*r*r*r/3.0;
            textBox2.Text=l.ToString();
            textBox3.Text=s.ToString();
            textBox4.Text=v.To.String();
        }

我比较喜欢这样

谢谢啊,这样的写法挺不错的,简洁啊~

呵呵 我也新手 相互学习