Step:

•   Select Window from Installed Templates in Visual C#
•   Select Window From Control Library
•   Click OK

After click OK button new Window will appear, on user control  simply drag and drop four button on it and button will be “Add”,”Subtract”,”Multiply” and ”Division” as  shown below:

To create user control

Code:

public partial class UserControl1 :  UserControl
    {
         publicUserControl1()
         {
            InitializeComponent();
         }
         intnum1=0, num2=0, res=0;//declaring three member variables of int type
         Control ctrl1, ctrl2, ctrl3;//declaring three member variables of Control
         stringname1, name2;//declaring three member variables of string that will store textBox name
         private void UserControl1_Load(objectsender, EventArgse)
         {
         }
         public stringTextBoxName1//creating property for textBox
         {
             get
            {
                 return name1;//this line will return textBox name
            }
             set
            {
                name1=value;//this line will set textBox name
            }
         }
         public stringTextBoxName2//creating property for textBox
         {
             get
            {
                 return name2;//this line will return textBox name
            }
             set
            {
                name2=value;//this line will set textBox name
            }
         }
         private voidbtnAdd_Click(objectsender,  EventArgse)
         {
  
            ctrl1= (TextBox)FindForm().Controls[name1];//in this line FindForm() method will find textBox control from the Form where the name of textBox is  store in name1
            ctrl2= (TextBox)FindForm().Controls[name2];//in this line FindForm() method will find textBox control from the Form where the name of textBox is  store in name2
             if (ctrl1==null|| ctrl2==null)//checking condition 
            {
                 MessageBox.Show("TextBox can not blank");//it will show message
                 return;//return the execution
            }
             try//
            {
                MyControl();//this a function 
                res =num1+num2;//adding variable value and storing in res
                Display();//this a function 
  
            }
             catch (Exception ex)
            {
                 MessageBox.Show(ex.Message);//it will show message if exeception occurs
            }     
         }
         private voidbtnSub_Click(objectsender,  EventArgse)
         {
            ctrl1= (TextBox)FindForm().Controls[name1];
            ctrl2= (TextBox)FindForm().Controls[name2];
             if (ctrl1==null|| ctrl2==null)
            {
                 MessageBox.Show("TextBox can not blank");
                 return;
            }
             try
            {
                MyControl();
                res =num1-num2;//storing value in res after subtraction
                Display();
  
            }
             catch (Exception ex)
            {
                 MessageBox.Show(ex.Message);
            }  
         }
       
         private voidbtnDiv_Click(objectsender,  EventArgse)
         {
            ctrl1= (TextBox)FindForm().Controls[name1];
            ctrl2= (TextBox)FindForm().Controls[name2];
           
             if (ctrl1==null|| ctrl2==null)
            {
                 MessageBox.Show("TextBox can not blank");
                 return;
            }
             try
            {
                MyControl();
                res =num1/num2;//storing value in res after division
                Display();   
           
            }
             catch (Exception ex)
            {
                 MessageBox.Show(ex.Message);
            }
         } 
         private void UserControl1_Load_1(objectsender, EventArgse)
         {
            
         }      
         public voidMyControl()
         {
            ctrl3= (TextBox)FindForm().Controls["textBox3"];//in this line FindForm() method will find textBox control from the Form where the name of textBox is textBox3
            num1=Convert.ToInt32(ctrl1.Text);//Converting in integer and storing in num1
            num2=Convert.ToInt32(ctrl2.Text);//Converting in integer and storing in num2
         }
         public voidDisplay()
         {
            ctrl3.Text= Convert.ToString(res);//in this line res is storing as a text in textBox3
         }
  
         private voidbtnMul_Click_1(objectsender,  EventArgse)
         {
            ctrl1= (TextBox)FindForm().Controls[name1];
            ctrl2= (TextBox)FindForm().Controls[name2];
  
             if (ctrl1==null|| ctrl2==null)
            {
                 MessageBox.Show("TextBox can not blank");
                 return;
            }
             try
            {
                MyControl();
                res =num1*num2;//storing value in res after multiplication
                Display();
  
            }
             catch (Exception ex)
            {
                 MessageBox.Show(ex.Message);
            }
         }
    }
  

For adding user control in ToolBox:

Step:

•    Right  Click on the Toolbox
•    Select Choose Items

After the “Choose Items” new toolbox “Choose Toolbox items” will be open click on the browse button and you have to specify where user control folder is.

After Select user control folder follow this step:

•   Open folder
•   Open sub folder (bin)
•   Open bin sub folder (Debug)
•   Open  Debug folder
•   In Debug folder open  user control ( .dll)
•   Then click on OK

After that we can see user control(UserControl1) has added in ToolBox, when we want to use this user control simply drag and drop on the form as shown below:

This demonstration control can perform mathematical operation (Add, Subtract, Multiply and Divide) and result will be show in result TextBox as shown below.

Code

   public partial class Form1 :  Form
    {
         publicForm1()
         {
            InitializeComponent();
         }
         private void textBox1_TextChanged(objectsender, EventArgse)
         {
            userControl11.TextBoxName1=txtName1.Name;//this line will take textbox name and store in user control property TextBoxName1
         }
         private void textBox2_TextChanged(objectsender, EventArgse)
         {
            userControl11.TextBoxName2=txtName2.Name;//this line will take textbox name and store in user control property TextBoxName2
         }
         private voidForm1_Load(objectsender,  EventArgse)
         {
  
         }
         private void textBox3_TextChanged(objectsender, EventArgse)
         {
  
         }
        
         private void userControl11_Load_3(objectsender, EventArgse)
         {
  
         }
    }