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An exception of type 'System.FormatException' occurred in mscorlib.dll but was not handled in user code

Tag: c#,asp.net,visual-studio

I am attempting to multiply the values of dropDown to the user's inputted value in daysRenting. I am getting a format error with respect to the data types being used. dropDown uses doubles and daysRenting is an int. My problem lies in this line of code... How can I rewrite this to convert my data into the forms needed? The result will be a double. dropDown values are a daily charge for a selected car.

protected void button_Click(object sender, EventArgs e)
    {
    int i = Convert.ToInt32(dropDown.SelectedItem.Value.ToString()) * Convert.ToInt32(daysRenting.Text.ToString());
    totalCost.Text = i.ToString();
    }

Here's the full code for reference.

<%@ Page Language="C#" AutoEventWireup="true" CodeBehind="WebForm2.aspx.cs" Inherits="Assignment5.WebForm2" %>

<!DOCTYPE html>

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
</head>
<body>
<form id="form1" runat="server">
<div>

    <asp:DropDownList ID="dropDown" runat="server" AutoPostBack="True" OnSelectedIndexChanged="dropDown_SelectedIndexChanged">
        <asp:ListItem Value="null">Pick A Car Type</asp:ListItem>
        <asp:ListItem Value="29.99">Compact</asp:ListItem>
        <asp:ListItem Value="34.99">Intermediate</asp:ListItem>
        <asp:ListItem Value="24.99">Economy</asp:ListItem>
        <asp:ListItem Value="44.99">Standard</asp:ListItem>
        <asp:ListItem Value="49.99">Full Size</asp:ListItem>
    </asp:DropDownList>
    <br/><br/>
    Days Renting:<asp:TextBox ID="daysRenting" width="150px" runat="server" </asp:TextBox>
    <br /><br/>  
</div>
    <asp:Button ID="button" runat="server" Text="Submit" OnClick="button_Click" />
    <br/><br/>
    Total Cost:<asp:TextBox ID="totalCost" ReadOnly="true" runat="server" OnTextChanged="totalCost_TextChanged"></asp:TextBox>
</form>
</body>
</html>

and here's the .cs

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

namespace Assignment5
{
public partial class WebForm2 : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {

    }

    protected void dropDown_SelectedIndexChanged(object sender, EventArgs e)
    {

    }

    protected void button_Click(object sender, EventArgs e)
    {
    int i = Convert.ToInt32(dropDown.SelectedItem.Value.ToString()) * Convert.ToInt32(daysRenting.Text.ToString());
    totalCost.Text = i.ToString();
    }

    protected void totalCost_TextChanged(object sender, EventArgs e)
    {

    }
}
}

Best How To :

You can't parse those string representations of double values in the drop-down directly to int like that, hence the error. Internally, it's basically calling this, and it expects an integer:

Int32.Parse("29.99", NumberStyles.Integer, CultureInfo.CurrentCulture);

Convert the strings to double instead, then either use them like that or cast them to an int.

double i =
    Convert.ToDouble(dropDown.SelectedItem.Value) * Convert.ToInt32(daysRenting.Text);

totalCost.Text = i.ToString();

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