I have a simple Windows Forms application which is used to calculate the solutions to a quadratic equation. Since it requires some values to be inputted into three different textboxes and then upon clicking a “Calculate” button, makes some calculations with the inputted values. Upon testing the application, and clicking the “Calculate” button prior to inputting any values, I get a Input string was not in a correct format This is due to trying to parse a non-existent value. Is there any way to avoid this? I tried to construct a conditional based on if the button was clicked and there was no values in the textboxes, to not do anything, but that didn’t quite work. Here is my designer code:
namespace QuadraticSolver
{
partial class QuadraticSolver
{
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;
/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}
#region Windows Form Designer generated code
/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.lblPrompt = new System.Windows.Forms.Label();
this.lblA = new System.Windows.Forms.Label();
this.lblB = new System.Windows.Forms.Label();
this.lblC = new System.Windows.Forms.Label();
this.txtA = new System.Windows.Forms.TextBox();
this.txtB = new System.Windows.Forms.TextBox();
this.txtC = new System.Windows.Forms.TextBox();
this.btnCalculate = new System.Windows.Forms.Button();
this.lblSolutions = new System.Windows.Forms.Label();
this.txtSolution1 = new System.Windows.Forms.TextBox();
this.txtSolution2 = new System.Windows.Forms.TextBox();
this.chkImaginary = new System.Windows.Forms.CheckBox();
this.SuspendLayout();
//
// lblPrompt
//
this.lblPrompt.AutoSize = true;
this.lblPrompt.Location = new System.Drawing.Point(12, 9);
this.lblPrompt.Name = "lblPrompt";
this.lblPrompt.Size = new System.Drawing.Size(92, 13);
this.lblPrompt.TabIndex = 0;
this.lblPrompt.Text = "Enter Your Values";
//
// lblA
//
this.lblA.AutoSize = true;
this.lblA.Location = new System.Drawing.Point(12, 49);
this.lblA.Name = "lblA";
this.lblA.Size = new System.Drawing.Size(16, 13);
this.lblA.TabIndex = 1;
this.lblA.Text = "a:";
//
// lblB
//
this.lblB.AutoSize = true;
this.lblB.Location = new System.Drawing.Point(12, 85);
this.lblB.Name = "lblB";
this.lblB.Size = new System.Drawing.Size(16, 13);
this.lblB.TabIndex = 2;
this.lblB.Text = "b:";
//
// lblC
//
this.lblC.AutoSize = true;
this.lblC.Location = new System.Drawing.Point(12, 122);
this.lblC.Name = "lblC";
this.lblC.Size = new System.Drawing.Size(16, 13);
this.lblC.TabIndex = 3;
this.lblC.Text = "c:";
//
// txtA
//
this.txtA.Location = new System.Drawing.Point(34, 46);
this.txtA.Name = "txtA";
this.txtA.Size = new System.Drawing.Size(360, 20);
this.txtA.TabIndex = 4;
//
// txtB
//
this.txtB.Location = new System.Drawing.Point(34, 82);
this.txtB.Name = "txtB";
this.txtB.Size = new System.Drawing.Size(360, 20);
this.txtB.TabIndex = 5;
//
// txtC
//
this.txtC.Location = new System.Drawing.Point(34, 122);
this.txtC.Name = "txtC";
this.txtC.Size = new System.Drawing.Size(360, 20);
this.txtC.TabIndex = 6;
//
// btnCalculate
//
this.btnCalculate.Location = new System.Drawing.Point(175, 154);
this.btnCalculate.Name = "btnCalculate";
this.btnCalculate.Size = new System.Drawing.Size(75, 23);
this.btnCalculate.TabIndex = 7;
this.btnCalculate.Text = "Calculate!";
this.btnCalculate.UseVisualStyleBackColor = true;
this.btnCalculate.Click += new System.EventHandler(this.btnCalculate_Click);
//
// lblSolutions
//
this.lblSolutions.AutoSize = true;
this.lblSolutions.Location = new System.Drawing.Point(31, 226);
this.lblSolutions.Name = "lblSolutions";
this.lblSolutions.Size = new System.Drawing.Size(53, 13);
this.lblSolutions.TabIndex = 8;
this.lblSolutions.Text = "Solutions:";
//
// txtSolution1
//
this.txtSolution1.Location = new System.Drawing.Point(34, 242);
this.txtSolution1.Name = "txtSolution1";
this.txtSolution1.ReadOnly = true;
this.txtSolution1.Size = new System.Drawing.Size(165, 20);
this.txtSolution1.TabIndex = 9;
//
// txtSolution2
//
this.txtSolution2.Location = new System.Drawing.Point(222, 242);
this.txtSolution2.Name = "txtSolution2";
this.txtSolution2.ReadOnly = true;
this.txtSolution2.Size = new System.Drawing.Size(172, 20);
this.txtSolution2.TabIndex = 10;
//
// chkImaginary
//
this.chkImaginary.AutoSize = true;
this.chkImaginary.Location = new System.Drawing.Point(33, 189);
this.chkImaginary.Name = "chkImaginary";
this.chkImaginary.Size = new System.Drawing.Size(71, 17);
this.chkImaginary.TabIndex = 11;
this.chkImaginary.Text = "Imaginary";
this.chkImaginary.UseVisualStyleBackColor = true;
//
// QuadraticSolver
//
this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.ClientSize = new System.Drawing.Size(406, 285);
this.Controls.Add(this.chkImaginary);
this.Controls.Add(this.txtSolution2);
this.Controls.Add(this.txtSolution1);
this.Controls.Add(this.lblSolutions);
this.Controls.Add(this.btnCalculate);
this.Controls.Add(this.txtC);
this.Controls.Add(this.txtB);
this.Controls.Add(this.txtA);
this.Controls.Add(this.lblC);
this.Controls.Add(this.lblB);
this.Controls.Add(this.lblA);
this.Controls.Add(this.lblPrompt);
this.Name = "QuadraticSolver";
this.Text = "Quadratic Solver";
this.ResumeLayout(false);
this.PerformLayout();
}
#endregion
private System.Windows.Forms.Label lblPrompt;
private System.Windows.Forms.Label lblA;
private System.Windows.Forms.Label lblB;
private System.Windows.Forms.Label lblC;
private System.Windows.Forms.TextBox txtA;
private System.Windows.Forms.TextBox txtB;
private System.Windows.Forms.TextBox txtC;
private System.Windows.Forms.Button btnCalculate;
private System.Windows.Forms.Label lblSolutions;
private System.Windows.Forms.TextBox txtSolution1;
private System.Windows.Forms.TextBox txtSolution2;
private System.Windows.Forms.CheckBox chkImaginary;
}
}
Here is my program’s code which does the actual data manipulation:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
namespace QuadraticSolver
{
public partial class QuadraticSolver : Form
{
public QuadraticSolver()
{
InitializeComponent();
}
private void btnCalculate_Click(object sender, EventArgs e)
{
if (txtA.Text == "" || txtB.Text == "" || txtC.Text == "")
{
string stringSol = "Please enter some values!";
txtSolution1.Text = stringSol;
txtSolution2.Text = stringSol;
}
double aValue = double.Parse(txtA.Text);
double bValue = double.Parse(txtB.Text);
double cValue = double.Parse(txtC.Text);
double solution1Double, solution2Double;
//Quadratic Formula: x = (-b +- sqrt(b^2 - 4ac)) / 2a
//Calculate discriminant
double insideSquareRoot = (bValue * bValue) - 4 * aValue * cValue;
if (insideSquareRoot < 0)
{
//No real solution
solution1Double = Double.NaN;
solution2Double = Double.NaN;
txtSolution1.Text = solution1Double.ToString();
txtSolution2.Text = solution2Double.ToString();
}
else if (insideSquareRoot == 0)
{
//One real solution
double sqrtOneSolution = Math.Sqrt(insideSquareRoot);
solution1Double = (-bValue + sqrtOneSolution) / (2 * aValue);
solution2Double = double.NaN;
txtSolution1.Text = solution1Double.ToString();
txtSolution2.Text = solution2Double.ToString();
}
else if (insideSquareRoot > 0)
{
//Two real solutions
double sqrtTwoSolutions = Math.Sqrt(insideSquareRoot);
solution1Double = (-bValue + sqrtTwoSolutions) / (2 * aValue);
solution2Double = (-bValue - sqrtTwoSolutions) / (2 * aValue);
txtSolution1.Text = solution1Double.ToString();
txtSolution2.Text = solution2Double.ToString();
}
}
}
}
You can use the
double.TryParsemethod.This is better than checking for
== ""since it will tell you that you can not parse “Hello” as a double too.You also need to return from the event handler if one of the
TryParsereturns false.