C# Area of Rectangle triangle and circle

This is a simple C# program code to find area of a rectangle, circle and triangle with user interface and example.

Manually we can find the area of a rectangle by using equation: 

  • Area = Breadth * Length. 
Also we can find the area of a circle by using equation: 

  • Area = 3.14 * (radius)2

Also we can find the area of a triangle by using equation: 

a = length of first side
b = length of second side
c = length of third side
s = (a + b+ c)/2

  • Area = sqrt(s*(s-a)*(s-b)*(s-c))

-where sqrt stands for square root

User interface with example

C# code Area of Rectangle triangle and circle

Here ‘Find Area’ is the ‘button_1’. There are three tabs: One is for ‘Rectangle’, another one is for ‘Triangle’ and last is for ‘Circle’.

Code Behind interface:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace area
    public partial class Form1 : Form
        public Form1()

        private void button1_Click(object sender, EventArgs e)
            if (tabControl1.SelectedTab == tabPage1)
                double breadth = Convert.ToDouble(textBox1.Text);
                double lenght = Convert.ToDouble(textBox2.Text);
                label5.Text = (breadth * lenght).ToString();
            if (tabControl1.SelectedTab == tabPage2)
                double a = Convert.ToDouble(textBox4.Text);
                double b = Convert.ToDouble(textBox5.Text);
                double c = Convert.ToDouble(textBox6.Text);
                double s = (a + b + c) / 2;
                double Area = Math.Sqrt(s * (s - a) * (s - b) * (s - c));
                label5.Text = (Area).ToString();
            if (tabControl1.SelectedTab == tabPage3)
                double  radius = Convert.ToDouble(textBox3.Text);
                label5.Text = (3.14 * radius).ToString();

  1. the code is good ,but i need the code without using tabs as per my requirement i need code by using textbox,button and list items (or) label can u make the code for it

  2. Instead of tabs, You can use listbox. Then add 3 items to listbox, named as 'Rectangle', Triangle' and 'Circle'.
    Now instead of tab selection code( if (tabControl1.SelectedTab == tabPage1) ) use list box control line:
    if(listbox1.text =="Rectangle")
    // Code for finding area of rectangle

    Like this, write code for finding area of triangle and circle


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