How to retrieve values of multiple txtBoxes and display sum in a new page?

Question

On Page1.aspx I have 3 txtBoxes with Compare Validators that ensure they are of type Currency.

On Page2.aspx I have another text box called txtResult whose job it is to display the sum of the other 3 txtBoxes when btnCalculate is clicked on Page1.

Problem: I can't get the 3 txtBoxes to be treated as doubles and not strings. If txtBox values are 1, 3, and 8, txtResult will be 138 and not 12.

I tried try parsing but it wasn't allowed failed to compile.

Code behind Page1:

protected void btnCalculate_Click(object sender, EventArgs e)
{
    if (IsValid)
    {
        Server.Transfer("Page2.aspx");
    }
}

Code behind Page2:

if (!IsPostBack)
{
    Page lastPage = (Page)Context.Handler;
    txtResult.Text = ((TextBox)lastPage.FindControl("txtGross")).Text
        + ((TextBox)lastPage.FindControl("txtValueOfAssets")).Text
        + ((TextBox)lastPage.FindControl("txtInvestments")).Text;
}

Attempt to use TryParse:

txtResult.Text = 
    double.TryParse(((TextBox)lastPage.FindControl("txtGross")).‌​Text, out gross);

Errors with:

Cannot implicitly covert bool to string

Answer 1

You can use Double.Parse(text) to convert the text into a double. So for example:

txtResult.Text = (Double.Parse(((TextBox)lastPage.FindControl("txtGross")).Text)
    + Double.Parse(((TextBox)lastPage.FindControl("txtValueOfAssets")).Text)
    + Double.Parse(((TextBox)lastPage.FindControl("txtInvestments")).Text)).ToString();

Notice that I needed to wrap the whole thing in a .ToString() to convert the answer back to text so that it can be assigned to txtResult.Text. I provided the answer in on long statement since the questions used one long statement but typically I convert each of the values to a double and place them in individual double vars then I'd add those in another statement, and finally in yet another statement I'd convert the answer to a string and place it in the text box. I find such a multi statement approach easier to read and digest, but that's just personal preference.

Answer 2

Text property of TextBox is a String type so adding them will result in concatenation. You need to convert the Text value to double before adding.

A simple way of converting is Convert.ToDouble("")

so try this: txtResult.Text = Convert.ToDouble(((TextBox)lastPage.FindControl("txtGross")).Text) + Convert.ToDouble(((TextBox)lastPage.FindControl("txtValueOfAssets")).Text) + Convert.ToDouble(((TextBox)lastPage.FindControl("txtInvestments")).Text);

Answer 3

Since your values are strings, they are being treated as strings, and are concatenating.

You need to convert those values to Double first, and then do your addition.

This post here talks about a few methods for converting to double: Converting string to double in C#

In essence, you can use the Convert.ToDouble() method to convert your text box Text value, to a double.

Convert.ToDouble(((TextBox)lastPage.FindControl("txtValueOfAssets")).Text)

The best approach, would be to look into the TryParse() method, to ensure that your code doesn't break if fed a non-numeric string.