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:

publicpartialclassUserControl1 : UserControl
    {
        publicUserControl1()
        {
            InitializeComponent();
        }
        intnum1=0, num2=0, res=0;//declaring three member variables of int type
        Controlctrl1, ctrl2, ctrl3;//declaring three member variables of Control
        stringname1, name2;//declaring three member variables of string that will store textBox name
        privatevoid UserControl1_Load(objectsender, EventArgse)
        {
        }
        publicstringTextBoxName1//creating property for textBox
        {
            get
            {
                 returnname1;//this line will return textBox name
            }
            set
            {
                name1=value;//this line will set textBox name
            }
        }
        publicstringTextBoxName2//creating property for textBox
        {
            get
            {
                 returnname2;//this line will return textBox name
            }
            set
            {
                name2=value;//this line will set textBox name
            }
        }
        privatevoidbtnAdd_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 (Exceptionex)
            {
                MessageBox.Show(ex.Message);//it will show message if exeception occurs
            }     
        }
        privatevoidbtnSub_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 (Exceptionex)
            {
                MessageBox.Show(ex.Message);
            }  
        }
       
        privatevoidbtnDiv_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 (Exceptionex)
            {
                MessageBox.Show(ex.Message);
            }
        } 
        privatevoid UserControl1_Load_1(objectsender, EventArgse)
        {
            
        }      
        publicvoidMyControl()
        {
            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
        }
        publicvoidDisplay()
        {
            ctrl3.Text= Convert.ToString(res);//in this line res is storing as a text in textBox3
        }
  
        privatevoidbtnMul_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 (Exceptionex)
            {
                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

  publicpartialclassForm1 : Form
    {
        publicForm1()
        {
            InitializeComponent();
        }
        privatevoid textBox1_TextChanged(objectsender, EventArgse)
        {
            userControl11.TextBoxName1=txtName1.Name;//this line will take textbox name and store in user control property TextBoxName1
        }
        privatevoid textBox2_TextChanged(objectsender, EventArgse)
        {
            userControl11.TextBoxName2=txtName2.Name;//this line will take textbox name and store in user control property TextBoxName2
        }
        privatevoidForm1_Load(objectsender, EventArgse)
        {
  
        }
        privatevoid textBox3_TextChanged(objectsender, EventArgse)
        {
  
        }
        
        privatevoid userControl11_Load_3(objectsender, EventArgse)
        {
  
        }
    }