C# Calculator Using Windows Forms
By S. Thangaraju

This is a basic calculator program using Windows Forms. You will be able to do mathematical operations like addition,subtraction etc.

Source Code

using System;
using System.Windows.Forms;
using System.Drawing;

public class win:Form {

  Button[] b = new Button[10];
  Button bDot,bPlus,bSub,bMul,bDiv,bEqu,bClr;
  Panel panCalc;
  TextBox txtCalc;
  
  Double dblAcc;
  Double dblSec;
  bool blnClear,blnFrstOpen;
  String strOper;
  
  public win() {
     try {
    this.Text="Calculator";
    panCalc=new Panel();
    txtCalc = new TextBox();

    txtCalc.Location = new Point(10,10);
    txtCalc.Size=new Size(150,10);
    txtCalc.ReadOnly=true;
    txtCalc.RightToLeft=RightToLeft.Yes;
    panCalc.Size=new Size(200,200);
    panCalc.BackColor=Color.Aqua;
    panCalc.Controls.Add(txtCalc);
    addButtons(panCalc);
    this.Size=new Size(200,225);
    this.Controls.Add(panCalc);
    
    dblAcc=0;
    dblSec=0;
    blnFrstOpen=true;
    blnClear=false;
    strOper=new String('=',1);
      }
      catch (Exception e) {
    Console.WriteLine("error ......  " + e.StackTrace);
      }
  }
  
  private void addButtons(Panel p) {
    for (int i=0;i<=9;i++) {
      b[i]=new Button();
      b[i].Text=Convert.ToString(i);
      b[i].Size=new Size(25,25);
      b[i].BackColor=Color.White;
      b[i].Click+=new EventHandler(btn_clk);
      p.Controls.Add(b[i]);  
    }
    b[0].Location=new Point(10,160);
    b[1].Location=new Point(10,120);
    b[4].Location=new Point(10,80);
    b[7].Location=new Point(10,40);
    
    b[2].Location=new Point(50,120);
    b[5].Location=new Point(50,80);
    b[8].Location=new Point(50,40);
    
    b[3].Location=new Point(90,120);
    b[6].Location=new Point(90,80);
    b[9].Location=new Point(90,40);
    
    bDot=new Button();
    bDot.Size=new Size(25,25);
    bDot.Location=new Point(50,160);
    bDot.BackColor=Color.White;
    bDot.Text=".";
    bDot.Click+=new EventHandler(btn_clk);
    
    bPlus=new Button();
    bPlus.Size=new Size(25,25);
    bPlus.Location=new Point(130,160);
    bPlus.BackColor=Color.White;
    bPlus.Text="+";
    bPlus.Click+=new EventHandler(btn_Oper);
    
    bSub=new Button();
    bSub.Size=new Size(25,25);
    bSub.Location=new Point(130,120);
    bSub.BackColor=Color.White;
    bSub.Text="-";
    bSub.Click+=new EventHandler(btn_Oper);
    
    bMul=new Button();
    bMul.Size=new Size(25,25);
    bMul.Location=new Point(130,80);
    bMul.BackColor=Color.White;
    bMul.Text="*";
    bMul.Click+=new EventHandler(btn_Oper);
    
    bDiv=new Button();
    bDiv.Size=new Size(25,25);
    bDiv.Location=new Point(130,40);
    bDiv.BackColor=Color.White;
    bDiv.Text="/";
    bDiv.Click+=new EventHandler(btn_Oper);
    
    bEqu=new Button();
    bEqu.Size=new Size(25,25);
    bEqu.Location=new Point(90,160);
    bEqu.BackColor=Color.White;
    bEqu.Text="=";
    bEqu.Click+=new EventHandler(btn_equ);
    
    bClr=new Button();
    bClr.Size=new Size(20,45);
    bClr.Location=new Point(170,40);
    bClr.BackColor=Color.Orange;
    bClr.Text="AC";
    bClr.Click+=new EventHandler(btn_clr);

    p.Controls.Add(bDot);
    p.Controls.Add(bPlus);
    p.Controls.Add(bSub);
    p.Controls.Add(bMul);
    p.Controls.Add(bDiv);
    p.Controls.Add(bEqu);
    p.Controls.Add(bClr);
  }
  
  private void btn_clk(object obj,EventArgs ea) {
    if(blnClear)
      txtCalc.Text="";
    
    Button b3=(Button)obj;
    
    txtCalc.Text+=b3.Text;  
    
    if (txtCalc.Text==".")
      txtCalc.Text="0.";
    dblSec=Convert.ToDouble(txtCalc.Text);
    
    blnClear=false;
  }
  
  private static void Main() {
    Application.Run(new win());
  }
  
  private void btn_Oper(object obj,EventArgs ea) {
    Button tmp=(Button)obj;
    strOper=tmp.Text;
    if (blnFrstOpen)
      dblAcc=dblSec;
    else
      calc();

    blnFrstOpen=false;
    blnClear=true;
  }

  private void btn_clr(object obj,EventArgs ea) {
    clear();
  }

  private void btn_equ(object obj,EventArgs ea) {
    calc();
    
  }
  
  private void calc() {

    switch(strOper) {
    
      case "+":
        dblAcc+=dblSec;
        break;
      case "-":
        dblAcc-=dblSec;
        break;
      case "*":
        dblAcc*=dblSec;
        break;
      case "/":
        dblAcc/=dblSec;
        break;
    }
  
    strOper="=";
    blnFrstOpen=true;
    txtCalc.Text=Convert.ToString(dblAcc);
    dblSec=dblAcc;
  }
  
  private void clear() {
    dblAcc=0;
    dblSec=0;
    blnFrstOpen=true;
    txtCalc.Text="";
    txtCalc.Focus();

  }
}