计算器

            bool a; //判断上一次按键是加减乘除还是数字
            string c = ""; //判断加减乘除操作
            decimal f;//记录第一个值以及接收运算结果
            /// <summary>
            /// 数字按键
            /// </summary>
            /// <param name="sender"></param>
            /// <param name="e"></param>
            private void button1_Click(object sender, EventArgs e)
            {
                Button b = sender as Button;
                if (textBox2.Text == "0" || a == false)
                {
                    textBox2.Text = b.Text;
                }
                else
                {
                    textBox2.Text += b.Text;
                }
                if (textBox1.Text == "")
                {
                    f = Convert.ToDecimal(textBox2.Text);
                }
                a = true;
            }
            /// <summary>
            /// 加减乘除
            /// </summary>
            /// <param name="sender"></param>
            /// <param name="e"></param>
            private void button4_Click(object sender, EventArgs e)
            {
                Button b = sender as Button;
                if (textBox2.Text.LastIndexOf(".") == (textBox2.Text.Length - 1))
                {
                    textBox2.Text = textBox2.Text.Substring(0, (textBox2.Text.Length - 1));
                }           
                if (a == false)
                {
                    textBox1.Text = textBox1.Text.Substring(0, (textBox1.Text.Length - 1)) + b.Text;
                }
                else
                {
                    textBox1.Text += textBox2.Text + b.Text;
                    if (c == "1")
                    {
                        f = f + Convert.ToDecimal(textBox2.Text);
                    }
                    else if (c == "2")
                    {
                        f = f - Convert.ToDecimal(textBox2.Text);
                    }
                    else if (c == "3")
                    {
                        f = f * Convert.ToDecimal(textBox2.Text);
                    }
                    else if (c == "4")
                    {
                        f = f / Convert.ToDecimal(textBox2.Text);
                    }
                    textBox2.Text = f.ToString();
                }
                if (b.Text == "+")
                {
                    c = "1";
                }
                else if (b.Text == "-")
                {
                    c = "2";
                }
                else if (b.Text == "*")
                {
                    c = "3";
                }
                else if (b.Text == "/")
                {
                    c = "4";
                }
                a = false;
            }
            /// <summary>
            /// 点
            /// </summary>
            /// <param name="sender"></param>
            /// <param name="e"></param>
            private void button17_Click(object sender, EventArgs e)
            {
                if (textBox2.Text.Contains(".") == false)
                {
                    textBox2.Text += ".";
                }
            }
            /// <summary>
            /// 等于
            /// </summary>
            /// <param name="sender"></param>
            /// <param name="e"></param>
            private void button15_Click(object sender, EventArgs e)
            {
                if (textBox2.Text.LastIndexOf(".") == (textBox2.Text.Length - 1))
                {
                    textBox2.Text = textBox2.Text.Substring(0, (textBox2.Text.Length - 1));
                }
                if (c == "1")
                {
                    f = f + Convert.ToDecimal(textBox2.Text);
                }
                else if (c == "2")
                {
                    f = f - Convert.ToDecimal(textBox2.Text);
                }
                else if (c == "3")
                {
                    f = f * Convert.ToDecimal(textBox2.Text);
                }
                else if (c == "4")
                {
                    f = f / Convert.ToDecimal(textBox2.Text);
                }
                textBox1.Text = "";
                textBox2.Text = f.ToString();
            }
            /// <summary>
            /// 清空
            /// </summary>
            /// <param name="sender"></param>
            /// <param name="e"></param>
            private void button14_Click(object sender, EventArgs e)
            {
                textBox1.Text = "";
                textBox2.Text = "0";
                a = true;
                c = "";
            }