c#简单计算器 一个问题不懂。。
问题在代码注释中 为什么 用到bool 为什么在输出小数点的时候用到bool?



public partial class Form1 : Form
{
public Form1()
{
InitializeComponent();
}
double a, b, result;
string action;
bool isPoint; //为什么定义 这个bool

private void button3_Click(object sender, EventArgs e)//以下是定义按钮数字
{
textBox1_ShowNum.Text += "3";
}

private void button5_Click(object sender, EventArgs e)
{
textBox1_ShowNum.Text += "5";
}

private void button7_Click(object sender, EventArgs e)
{
textBox1_ShowNum.Text += "7";
}

private void button1_Click(object sender, EventArgs e)
{
textBox1_ShowNum.Text += "1";
}

private void button2_Click(object sender, EventArgs e)
{
textBox1_ShowNum.Text += "2";
}
private void button4_Click(object sender, EventArgs e)
{
textBox1_ShowNum.Text += "4";
}
private void button6_Click(object sender, EventArgs e)
{
textBox1_ShowNum.Text += "6";
}
private void button8_Click(object sender, EventArgs e)
{
textBox1_ShowNum.Text += "8";
}

private void button9_Click(object sender, EventArgs e)
{
textBox1_ShowNum.Text += "9";
}

private void button_13_0_Click(object sender, EventArgs e)
{
textBox1_ShowNum.Text += "0";
}

private void button12_point_Click(object sender, EventArgs e)
{
if (!isPoint)//这里if 中为什么用到bool 实现的是什么功能？ 为什么要 !isPoint 才 输出 "." 小数点
{
textBox1_ShowNum.Text += ".";
}
}

private void button10_加法_Click(object sender, EventArgs e)//以下是定义 加减乘除运算
{
if (textBox1_ShowNum.Text.Length != 0)
{
a = double.Parse(textBox1_ShowNum.Text);
}
else
{
a = 0;
}
action = "1";
textBox1_ShowNum.Text= " ";
}

private void button12_减法_Click(object sender, EventArgs e)
{
if (textBox1_ShowNum.Text.Length != 0)
{
a = double.Parse(textBox1_ShowNum.Text);
}
else
{
a = 0;
}
action = "2";
textBox1_ShowNum.Text= " ";
}
private void button14_乘_Click(object sender, EventArgs e)
{
if (textBox1_ShowNum.Text.Length != 0)
{
a = double.Parse(textBox1_ShowNum.Text);
}
else
{
a = 0;
}
action = "3";

textBox1_ShowNum.Text = " ";
}
private void button_除_Click(object sender, EventArgs e)
{
if (textBox1_ShowNum.Text.Length != 0)
{
a = double.Parse(textBox1_ShowNum.Text);
}
else
{
a = 0;
}
action = "4";
textBox1_ShowNum.Text = " ";
}

private void button11_等号_Click(object sender, EventArgs e)
{
if (textBox1_ShowNum.Text.Length != 0)
{
b = double.Parse(textBox1_ShowNum.Text);
}
else
{
b = 0;
}
switch (action)
{
case "1": result = a + b; break;
case "2": result = a - b; break;
case "3": result = a * b; break;
case "4":
if (b != 0)
{
result = a / b;
}
else
{
MessageBox.Show("错误");
}
break;
}
textBox1_ShowNum.Text = result.ToString();

}

private void Form1_Load(object sender, EventArgs e)
{

}



private void button17_归零_Click(object sender, EventArgs e)
{
textBox1_ShowNum.Text = " ";
}


}

[解决办法]
if (!isPoint)//这里if 中为什么用到bool 实现的是什么功能？ 为什么要 !isPoint 才 输出 "." 小数点
{
textBox1_ShowNum.Text += ".";
}
仅看这段代码就明白了，第一次按“.”按钮，isPoint为false，文本框文本末尾添加个.；然后可能把isPoint设为true，这样下次再按“.”按钮，就不会添加.了。

主要是保证文本框里的数值最多只有1个小数点。