c# - 使用 double 有问题，我被困在某个地方？

Question

我想给一个整数加上 0.50，只是我很困惑。我不知道该怎么办。这是代码；

if (checkBox1.Checked)
{
    keko.Open();

    double mesai = Convert.ToDouble(textBox4.Text);
    mesai = mesai + 0.50;
    double maaş = Convert.ToDouble(textBox4.Text);
    maaş += 1;
    textBox4.Text = mesai.ToString() + maaş.ToString();

    MySqlCommand cmd = new MySqlCommand(
      "Update calisanlist Set Gun '" + textBox4.Text + "' where (Adı,Soyadı) '" + textBox1.Text + "','"+textBox2.Text+"'", 
       keko);

    cmd.ExecuteNonQuery();

    keko.Close();

按钮下方有一个复选框。如果我按下按钮而不选中该框，它会自行添加 1 好吧，这里没有问题。但是，当我选中该框并按下按钮时，我收到一条错误消息。

MySql.Data.MySqlClient.MySqlException:

'You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near ''7,58' where (Adı,Soyadı) 'Egemen','Ören'' at line 1'.

我不知道如何解决，请帮助我

Answer 1

看来你很可能遇到了问题

   textBox4.Text = mesai.ToString() + maaş.ToString();

想象一下，mesai是 3.5当maaş是 4.1 :您将拥有3.54.1在 textBox4.Text这不是有效 double值(value)。你可能是说

   double mesai = Convert.ToDouble(textBox4.Text) + 0.5;
   //TODO: check isn't it a typo? Both mesai and maaş are from the same textBox4.Text
   double maaş = Convert.ToDouble(textBox4.Text) + 1;

   textBox4.Text = (mesai + maaş).ToString();

不要对查询进行硬编码，而是对其进行参数化

   ... 

   // Keep sql readable
   // and parameterized
   string sql = 
     @"update calisanlist
          set Gun = @prm_Gun
        where Adı = @prm_Adi and
              Soyadı = @prm_Soyadı";  

   // wrap IDisposable into "using"
   using (MySqlCommand cmd = new MySqlCommand(sql, keko)) {
     // I don't know underlying database types, that's why I've put AddWithValue
     //TODO: change syntax to cmd.Parameters.Add(name, datatype).Value = ...
     cmd.Parameters.AddWithValue("@prm_Gun", Convert.ToDouble(textBox4.Text));
     cmd.Parameters.AddWithValue("@prm_Adi", textBox1.Text);
     cmd.Parameters.AddWithValue("@prm_Soyadı", textBox2.Text); 

     cmd.ExecuteNonQuery();
   } 
   ...