C# Windows窗体C“；输入字符串的格式不正确"；

我有一个简单的Windows窗体应用程序，用于计算二次方程的解。因为它需要将一些值输入到三个不同的文本框中，然后单击“计算”按钮，使用输入的值进行一些计算。在测试应用程序并在输入任何值之前单击“计算”按钮后，我得到一个

输入字符串的格式不正确

这是由于试图解析一个不存在的值。有没有办法避免这种情况？我试图构建一个基于按钮是否被点击，文本框中是否没有值的条件，以不做任何事情，但这并不奏效。以下是我的设计器代码：

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;
    }
}

namespace QuadraticSolver
{
部分类二次解算器
{
/// 
///必需的设计器变量。
/// 
private System.ComponentModel.IContainer components=null；
/// 
///清理所有正在使用的资源。
/// 
///如果应释放托管资源，则为true；否则为false。
受保护的覆盖无效处置（布尔处置）
{
if（处理和（组件！=null））
{
组件。Dispose（）；
}
基地。处置（处置）；
}
#区域Windows窗体设计器生成的代码
/// 
///设计器支持所需的方法-不修改
///此方法的内容与代码编辑器一起使用。
/// 
私有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（）；
这个.SuspendLayout（）；
// 
//LBL提示
// 
this.lblPrompt.AutoSize=true；
this.lblPrompt.Location=新系统图纸点（12,9）；
this.lblPrompt.Name=“lblPrompt”；
this.lblPrompt.Size=新系统图纸尺寸（92,13）；
this.lblPrompt.TabIndex=0；
this.lblPrompt.Text=“输入您的值”；
// 
//lblA
// 
this.lblA.AutoSize=true；
this.lblA.Location=新系统图纸点（12,49）；
this.lblA.Name=“lblA”；
this.lblA.Size=新系统图纸尺寸（16,13）；
this.lblA.TabIndex=1；
this.lblA.Text=“a:”；
// 
//lblB
// 
this.lblB.AutoSize=true；
this.lblB.Location=新系统图纸点（12,85）；
this.lblB.Name=“lblB”；
this.lblB.Size=新系统图纸尺寸（16,13）；
this.lblB.TabIndex=2；
this.lblB.Text=“b:”；
// 
//lblC
// 
this.lblC.AutoSize=true；
this.lblC.Location=新系统图纸点（12，122）；
this.lblC.Name=“lblC”；
this.lblC.Size=新系统图纸尺寸（16,13）；
this.lblC.TabIndex=3；
this.lblC.Text=“c:”；
// 
//txtA
// 
this.txtA.Location=新系统图纸点（34,46）；
this.txtA.Name=“txtA”；
this.txtA.Size=新系统图纸尺寸（360,20）；
this.txtA.TabIndex=4；
// 
//txtB
// 
this.txtB.Location=新系统图纸点（34,82）；
this.txtB.Name=“txtB”；
this.txtB.Size=新系统图纸尺寸（360,20）；
this.txtB.TabIndex=5；
// 
//txtC
// 
this.txtC.Location=新系统图纸点（34122）；
this.txtC.Name=“txtC”；
this.txtC.Size=新系统图纸尺寸（360,20）；
this.txtC.TabIndex=6；
// 
//计算
// 
this.btnCalculate.Location=新系统图点（175154）；
this.btnCalculate.Name=“btnCalculate”；
this.btnCalculate.Size=新系统.图纸.尺寸（75,23）；
this.btnCalculate.TabIndex=7；
this.btnCalculate.Text=“计算！”；
this.btnCalculate.UseVisualStyleBackColor=true；
this.btnCalculate.Click+=新建System.EventHandler（this.btnCalculate\u Click）；
// 
//LBL解决方案
// 
this.lblSolutions.AutoSize=true；
this.lblSolutions.Location=新系统图点（31226）；
this.lblSolutions.Name=“lblSolutions”；
this.lblSolutions.Size=新系统图纸尺寸（53,13）；
this.lblSolutions.TabIndex=8；
this.lblSolutions.Text=“解决方案：”；
// 
//TXT解决方案1
// 
this.txtSolution1.Location=新系统图纸点（34242）；
this.txtSolution1.Name=“txtSolution1”；
this.txtSolution1.ReadOnly=true；
this.txtSolution1.Size=新系统图纸尺寸（165,20）；
this.txtSolution1.TabIndex=9；
// 
//TXT解决方案2
// 
this.txtSolution2.Location=新系统图点（222242）；
this.txtSolution2.Name=“txtSolu
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();
            }
        }
    }
}


if (txtA.Text == "" || txtB.Text == "" || txtC.Text == "")
            {
                string stringSol = "Please enter some values!";
                txtSolution1.Text = stringSol;
                txtSolution2.Text = stringSol;
                return;
            }

double userNumber = myNumUpDown.Value;

myNumUpDown.Minimum = 300;
myNumUpDown.Maximum = 500;

int a = textbox1.Text != "" ? Convert.ToInt32(textbox1.Text) : 0;
int b = textbox2.Text != "" ? Convert.ToInt32(textbox2.Text) : 0;
int total = a + b;

textbox3 = total.toString();