Question

OK, I have a problem where my calculation never takes place, like it is supposed to. i’m trying to make a computation which solves for the roots of a quadratic equation using the quadratic formula, based on the values of a, b and c entered in a primitive form.

Now, let me supply the code for my Model, view and Controller for this application:

Model:

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

namespace RootFinder.Models
{
    public class QuadCalc
    {
        public double quadraticAValue { get; set; }
        public double quadraticBValue { get; set; }
        public double quadraticCValue { get; set; }
        public double x1 { get; set; }
        public double x2 { get; set; }

        public void QuadCalculate(out double x1, out double x2)
        {
            //Quadratic Formula: x = (-b +- sqrt(b^2 - 4ac)) / 2a

            //Calculate the inside of the square root
            double insideSquareRoot = (quadraticBValue * quadraticBValue) - 4 * quadraticAValue * quadraticCValue;

            if (insideSquareRoot < 0)
            {
                //There is no solution
                x1 = double.NaN;
                x2 = double.NaN;
            }
            else
            {
                //Compute the value of each x
                //if there is only one solution, both x's will be the same
                double sqrt = Math.Sqrt(insideSquareRoot);
                x1 = (-quadraticBValue + sqrt) / (2 * quadraticAValue);
                x2 = (-quadraticBValue - sqrt) / (2 * quadraticAValue);
            }
        }
    }
}

View:

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<dynamic>" %>

<asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
Polynomial Root Finder - Quadratic
</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
    <h2>Quadratic</h2>

    <% using(Html.BeginForm("Quadratic", "Calculate")) %>
    <% { %>
    <div>
        a: <%= Html.TextBox("quadraticAValue") %>
        <br />
        b: <%= Html.TextBox("quadraticBValue") %>
        <br />
        c: <%= Html.TextBox("quadraticCValue") %>
        <br />
        <input type="submit" id="quadraticSubmitButton" value="Calculate!" />
        <br />
        <p><%= ViewData["Root1"] %></p>
        <p><%= ViewData["Root2"] %></p>
    </div>
    <% } %>
</asp:Content>

Controller:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Web;
using System.Web.Mvc;
using RootFinder.Models;

namespace RootFinder.Controllers
{
    public class CalculateController : Controller
    {
        //
        // GET: /Calculate/

        public ActionResult Index()
        {
            return View();
        }

        [AcceptVerbs(HttpVerbs.Get)]
        public ViewResult Quadratic()
        {
            ViewData["Root1"] = "";
            ViewData["Root2"] = "";
            return View();
        }

        [AcceptVerbs(HttpVerbs.Post)]
        public ViewResult Quadratic(QuadCalc newQuadCalc)
        {
            ViewData["Root1"] = newQuadCalc.x1;
            ViewData["Root2"] = newQuadCalc.x2;
            return View();
        }

        public ActionResult Quartic()
        {
            return View();
        }

        public object x1 { get; set; }

        public object x2 { get; set; }
    }
}

Now, I’m trying to still work this out, but I believe the problem may lie in the assigning of the inputted values from the form, into a new object for computation. This could also be a problem considering that MVC will probably take in the form input a string stype, instead of a double, where in my model, I perform computations based off of the input being a double type.

I do not know where to make the string to double conversion if this even is necessary however.

Does anyone see why there is a problem.

The page outputs the following:

x1 = 0
x2 = 0

Answer 1

You never call the QuadCalculate method.

Beside of this I would suggest to move out the QuadCalculate from the view model. This latest advice does not affect in any way the actual answer. It’s just a respectful way of implementing the MVC pattern.

For example:

Your model class

public class QuadCalc {
    public double quadraticAValue { get; set; }
    public double quadraticBValue { get; set; }
    public double quadraticCValue { get; set; }
    public double x1 { get; set; }
    public double x2 { get; set; }
}

and your controller methods

[AcceptVerbs(HttpVerbs.Post)]
public ViewResult Quadratic(QuadCalc newQuadCalc) {
    // move your calculation method here or, better,
    // to a class that implements the repository pattern
    // do the calculation and then set the x1 and x2 members of 
    // your model class
    // You dont even need to use ViewData for this, just return 
    // back your model class to your view
    return View( newQuadCalc );
}

You can then transform your view in a strong-typed view and use your model class inside it

<%@ Page Title="" Language="C#" MasterPageFile="~/Views/Shared/Site.Master" Inherits="System.Web.Mvc.ViewPage<RootFinder.Models.QuadCalc>" %>

<asp:Content ID="Content1" ContentPlaceHolderID="TitleContent" runat="server">
Polynomial Root Finder - Quadratic
</asp:Content>

<asp:Content ID="Content2" ContentPlaceHolderID="MainContent" runat="server">
    <h2>Quadratic</h2>

    <% using(Html.BeginForm("Quadratic", "Calculate")) %>
    <% { %>
    <div>
        a: <%= Html.TextBox(Model.quadraticAValue) %>
        <br />
        b: <%= Html.TextBox(Model.quadraticBValue) %>
        <br />
        c: <%= Html.TextBox(Model.quadraticCValue) %>
        <br />
        <input type="submit" id="quadraticSubmitButton" value="Calculate!" />
        <br />
        <p><%= Model.x1 %></p>
        <p><%= Model.x2 %></p>
    </div>
    <% } %>
</asp:Content>

Less magic strings, if you change a property name you can get a compile time error (if you enable view compilation), cleaner code and many other advantage are just waiting for you! 🙂