Button doesn't make value appear in textBox

Question

I want 2 textBoxes to show numbers after I press a button, but when I press a button, one textBox shows number in it and the second doesn't.

    private void Calculating(object sender, EventArgs e)
    {
        if (textBox6.Text != "")
        {
           rutr = Double.Parse(textBox6.Text);
           rutd = rutr * 2;            
           textBox7.Text = (rutd).ToString();
           textBox8.Text = (3 / 4 * pi * rutr * rutr * rutr).ToString();
        }
    }

The textBox8 doesn't show correct number.

Answer 1

The very cause of the misbehavior is integer division : 3 / 4 == 0 should be

// The formula seems to be a volume of a sphere: 3/4 * Pi * r**3 
// It's a physical world, that's why 3.0 - double, not 3M - decimal 
textBox8.Text = (3.0 / 4.0 * pi * rutr * rutr * rutr).ToString();

please, notice floating point 3.0 value instead of integer 3 . Another suggestion is to use double.TryParse : if we can parse user input ( textBox6.Text ) then do it and compute

private void Calculating(object sender, EventArgs e) {
  double rutr = 0.0;

  // If we can parse textBox6.Text into double rutr  
  if (double.TryParse(textBox6.Text, out rutr)) {
    rutd = rutr * 2;            
    textBox7.Text = (rutd).ToString();
    textBox8.Text = (3.0 / 4.0 * pi * rutr * rutr * rutr).ToString(); 
  }
}

Edit : Technically, it's possible to produce blank ( "" ) in the textBox8 , see comments below (it's an interesting problem itself). Here's the code

    using System.Globalization;

    ...

    CultureInfo ci = (CultureInfo.CurrentCulture.Clone() as CultureInfo);

    // The idea: double.NaN will be displayed as blank 
    ci.NumberFormat.NaNSymbol = "";   

    CultureInfo.CurrentCulture = ci;  

    double pi = Math.Sqrt(-1); // pi is double.NaN - imaginary unit 

    ...

    // 0 * NaN * rutr * rutr * rutr == NaN which is printed as empty string
    textBox8.Text = (3 / 4 * pi * rutr * rutr * rutr).ToString(); 

Here we exploit the fact that, 0 * double.NaN == double.NaN . However, I don't believe in this kind of error

Answer 2

You should use a suffix to tell the compiler that the numeric literals are not treated as int.

textBox8.Text = (3M / 4M * pi * rutr * rutr * rutr).ToString();

https://docs.microsoft.com/en-US/dotnet/csharp/language-reference/keywords/decimal

Here is a list of possible suffixes:

F: float D: double U: uint L: long UL: ulong M: decimal