Cannot implicity convert type 'double' to 'string'

I am making a program to take the radius of a circle and output the diameter, area, and circumference. I’m trying to start with the diameter, but I keep receiving the error: Cannot implicitly convert type ‘double’ to ‘string.’ I’ve done similar programs using integers, but I can’t figure out for the life of me, how to receive floats in text boxes and calculate them so I can output them. This is my code so far.

<%@ Page Language="C#" %>
<!DOCTYPE html>
<script runat="server">
 protected void Button1_Click(object sender, EventArgs e)
 {
 double pi = 3.14159;
 lblDiameter.Text = (double.Parse(radius.Text)) * (double.Parse(radius.Text));
 } 
</script>

<html xmlns="http://www.w3.org/1999/xhtml">
<head id="Head1" runat="server">
 <title>Circles</title>
</head>

<body>
<form id="form1" runat="server">
    <div>
    <asp:TextBox
    id="radius"
     Runat="server" /> 
    <br /> 

    <asp:Button
    id="Button1"
    Text="Calculate"
    OnClick="Button1_Click" 
    Runat="server" />

    <asp:Label
    id="lblDiameter"
    Runat="server" />
</div>
</form>
</body>
</html>

Where am I going wrong?

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Answers:

Method 1

Method 2

Method 3

Answers:

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Method 1

You’re probably just missing a .ToString():

lblDiameter.Text = (double.Parse(radius.Text) * double.Parse(radius.Text)).ToString();

It’d be clearer and you’d avoid parsing the string twice by storing the number in a local variable:

var value = double.Parse(radius.Text);
lblDiameter.Text = (value * value).ToString();

Now, is a diameter really equal to the square of the radius? 😉

Method 2

You are getting the error because you are dealing with double data type on the right side of the equation and a string on the left.

Change your code from:

lblDiameter.Text = (double.Parse(radius.Text)) * (double.Parse(radius.Text));

To:

lblDiameter.Text = Convert.ToString((double.Parse(radius.Text)) * (double.Parse(radius.Text)));

or:

lblDiameter.Text = (double.Parse(radius.Text) * (double.Parse(radius.Text)).ToString();

or:

double radius = double.Parse(textBox1.Text);
lblDiameter.Text = (radius * radius).ToString();

Also you do not need to set pi. There is a constant in the Math namespace.

double pi = Math.PI;

I also suggest set a radius variable to use over again instead of doing (double.Parse(radius.Text) each time. Like in my example above.

double radius = double.Parse(textBox1.Text);

Then you can do things like:

lblDiameter.Text = Convert.ToString(radius * radius);

and:

lblDiameter.Text = (radius * radius).ToString();

Also:

double circum = (2 * pi) * radius;

Method 3

On the line of code lblDiameter.Text = (double.Parse(radius.Text)) * (double.Parse(radius.Text));

The left hand side lblDiameter.Text is considered a string and the right hand side is a double, as you parsed the value of the textbox to a double.

Here’s what you should do:

 double diameter = 0;

 diameter = double.Parse(radius.Text) * double.Parse(radius.Text);

Now after the equation, you can assign the value of “diameter” to lblDiameter, but you have to convert it to String:

lblDiameter.Text = diameter.ToString();

If you prefer, you can use only 2 lines of codes like below:

 double diameter = double.Parse(radius.Text) * double.Parse(radius.Text);
 lblDiameter.Text = diameter.ToString();

All methods was sourced from stackoverflow.com or stackexchange.com, is licensed under cc by-sa 2.5, cc by-sa 3.0 and cc by-sa 4.0

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