Ввод переменной из textBox и вывод ее в messageBox

#pragma once
 
namespace Project11 {
 
    using namespace System;
    using namespace System::ComponentModel;
    using namespace System::Collections;
    using namespace System::Windows::Forms;
    using namespace System::Data;
    using namespace System::Drawing;
 
    /// <summary>
    /// Summary for MyForm
    /// </summary>
    public ref class MyForm : public System::Windows::Forms::Form
    {
    public:
        MyForm(void)
        {
            InitializeComponent();
            //
            //TODO: Add the constructor code here
            //
        }
 
    protected:
        /// <summary>
        /// Clean up any resources being used.
        /// </summary>
        ~MyForm()
        {
            if (components)
            {
                delete components;
            }
        }
    private: System::Windows::Forms::TextBox^  textBox1;
    private: System::Windows::Forms::Button^  button1;
    protected:
 
    private:
        /// <summary>
        /// Required designer variable.
        /// </summary>
        System::ComponentModel::Container ^components;
 
#pragma 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>
        void InitializeComponent(void)
        {
            this->textBox1 = (gcnew System::Windows::Forms::TextBox());
            this->button1 = (gcnew System::Windows::Forms::Button());
            this->SuspendLayout();
            // 
            // textBox1
            // 
            this->textBox1->Location = System::Drawing::Point(82, 43);
            this->textBox1->Name = L"textBox1";
            this->textBox1->Size = System::Drawing::Size(100, 20);
            this->textBox1->TabIndex = 0;
            this->textBox1->TextChanged += gcnew System::EventHandler(this, &MyForm::textBox1_TextChanged);
            // 
            // button1
            // 
            this->button1->Location = System::Drawing::Point(82, 148);
            this->button1->Name = L"button1";
            this->button1->Size = System::Drawing::Size(100, 23);
            this->button1->TabIndex = 1;
            this->button1->Text = L"button1";
            this->button1->UseVisualStyleBackColor = true;
            this->button1->Click += gcnew System::EventHandler(this, &MyForm::button1_Click);
            // 
            // MyForm
            // 
            this->AutoScaleDimensions = System::Drawing::SizeF(6, 13);
            this->AutoScaleMode = System::Windows::Forms::AutoScaleMode::Font;
            this->ClientSize = System::Drawing::Size(284, 261);
            this->Controls->Add(this->button1);
            this->Controls->Add(this->textBox1);
            this->Name = L"MyForm";
            this->Text = L"MyForm";
            this->ResumeLayout(false);
            this->PerformLayout();
 
        }
#pragma endregion
    private: System::Void button1_Click(System::Object^  sender, System::EventArgs^  e) {
                int a = System::Int32::Parse(textBox1->Text);
                int b = a + 3;
 
    }
    private: System::Void textBox1_TextChanged(System::Object^  sender, System::EventArgs^  e) {
                 
    }
    };
}

MessageBox::Show(b.ToString());