This calculator can perform all the basic mathematical operations, like add, subtract, multiply and divide. It has a text box with displays input and output.

##### Objects name

Form: frmCalc

Text Box: txtDisp

Digits buttons: btn0, btn1,………., btn9

Subtract button: btnSub

Multiply button: btnMul

Divide button: btnDiv

Decimal button: btnPnt

Equal button: btnEql

Clear button: btnClear

##### Form Code with Explanation

`        double val; //it’ll store the result of the operations performed        public char prevOperator; //it’ll store the recent used operator                       //The function below will display the value in the text box according to the digits button pressed.        private void display(string sNum)        {         //checking whether the last used operator was ‘=’ or not. If it is equal then        //text box will be cleared for the new values to be displayed.             if (prevOperator == '=')            {                prevOperator = ' ';                txtDisp.Text = "";            }                    //checking whether the text box is empty. If text box is empty then value of        //pressed button will be displayed directly otherwise button text will be        //concatinated with the text box value           if(txtDisp.Text=="")                txtDisp.Text = sNum;            else                txtDisp.Text=txtDisp.Text + sNum;                    }         // initilizing the value of ‘val’ and ‘prevOperator’ at form load event.         private void Form1_Load(object sender, EventArgs e)        {            val = 0.0;                      prevOperator = ' ';        }         private void btn_Click(object sender, EventArgs e)        {         //calling display function and passing the text of button clicked as string             display(((Button)sender).Text);           }         private void btnAdd_Click(object sender, EventArgs e)        {        //setting the prevOperator to ‘+’ and adding the value of text box        //to value of ‘val’            prevOperator = '+';            val = val + Convert.ToDouble(txtDisp.Text);            txtDisp.Text = "";                                }         private void btnEql_Click(object sender, EventArgs e)        {                        if (prevOperator == '+')                                     val = val + Convert.ToDouble(txtDisp.Text);                        else if (prevOperator == '-')                val = val - Convert.ToDouble(txtDisp.Text);            else if (prevOperator == '*')                val = val * Convert.ToDouble(txtDisp.Text);            else if (prevOperator == '/')            {                try                {                    val = val / Convert.ToDouble(txtDisp.Text);                }                catch (Exception ex)                {                    MessageBox.Show(ex.Message);                }            }            txtDisp.Text = Convert.ToString(val);            prevOperator = '=';            val = 0.0;        }         private void btnSub_Click(object sender, EventArgs e)        {        //setting the prevOperator to ‘-’ and subtracting the value of text box        //from ‘val’             prevOperator = '-';            if (val == 0)                     val = Convert.ToDouble(txtDisp.Text);            else                val = val - Convert.ToDouble(txtDisp.Text);            txtDisp.Text = "";          }         private void btnMul_Click(object sender, EventArgs e)        {         //setting the prevOperator to ‘*’ and adding the value of text box         //to value of ‘val’             prevOperator = '*';            if (val == 0)                val = Convert.ToDouble(txtDisp.Text);            else                val = val * Convert.ToDouble(txtDisp.Text);                        txtDisp.Text = "";          }         private void btnDiv_Click(object sender, EventArgs e)        {         //setting the prevOperator to ‘/’ and adding the value of text box        //to value of ‘val’             prevOperator = '/';            if (val == 0)                val = Convert.ToDouble(txtDisp.Text);            else                val = val / Convert.ToDouble(txtDisp.Text);            txtDisp.Text = "";          }         private void btnPnt_Click(object sender, EventArgs e)        {            if (prevOperator == '=')            {                prevOperator = ' ';                txtDisp.Text = "";            }           //checking whether ‘.’ Is present in text box or not if present then no          //action will be taken as there can be only one decimal point in a number          //and if not then decimal will be added.             if (!txtDisp.Text.Contains('.'))            {          //checking whether text box contains any number or not. If not the ‘0.’        //Displayed otherwise decimal will be added to the number present        //in the text box.                if (txtDisp.Text != "")                    txtDisp.Text = txtDisp.Text + ".";                                else                    txtDisp.Text = "0.";            }                        }         private void btnClear_Click(object sender, EventArgs e)        {         //clearing the tex box.                     txtDisp.Text = "";}`

##### Sceen Shot
Modified On Nov-30-2017 06:21:50 AM