Question

The factorial of a non negative integer n is written n! and is defined as follows: n! = n · (n – 1) · (n – 2) · … · 1 (for values of n greater than 1) and n! = 1 (for n = 0 or n = 1).

For example, 5! = 5 · 4 · 3 · 2 · 1, which is 120. Use while statements in each of the following:

Write a C# Windows Forms Application that reads n from a textbox and display 1! through n! in a list box. Also, estimates the value of the mathematical constant e by using the following formula (with accuracy of 6 decimal places) :        

                                e = 1 + 1/1! + 1/2! + 1/3! + ...

Answer 1

Here is code:

NumberSeries.cs:

using System;
using System.Windows.Forms;

namespace WindowsFormsApp
{
public partial class NumberSeries : Form
{
public NumberSeries()
{
InitializeComponent();
}

private void btnCalculate_Click(object sender, EventArgs e)
{
int value = int.Parse(txtInput.Text);
if(value < 1)
{
MessageBox.Show("Input must be positive number");
}
else
{
double result = 0;
for (int i = 0; i < value; i++)
{
result += (1.0/factorial(i));
}
lbOutput.Text = "Result is " + result.ToString("#.######");
}
}

private double factorial(int n)
{
double prod = 1;
for (int i = 1; i <= n; i++)
{
prod *= i;
}
return prod;
}
}
}

NumberSeries.Designer.cs:

namespace WindowsFormsApp
{
partial class NumberSeries
{
/// <summary>
/// Required designer variable.
/// </summary>
private System.ComponentModel.IContainer components = null;

/// <summary>
/// Clean up any resources being used.
/// </summary>
/// <param name="disposing">true if managed resources should be disposed; otherwise, false.</param>
protected override void Dispose(bool disposing)
{
if (disposing && (components != null))
{
components.Dispose();
}
base.Dispose(disposing);
}

#region Windows Form Designer generated code

/// <summary>
/// Required method for Designer support - do not modify
/// the contents of this method with the code editor.
/// </summary>
private void InitializeComponent()
{
this.label1 = new System.Windows.Forms.Label();
this.txtInput = new System.Windows.Forms.TextBox();
this.btnCalculate = new System.Windows.Forms.Button();
this.lbOutput = new System.Windows.Forms.Label();
this.SuspendLayout();
//
// label1
//
this.label1.AutoSize = true;
this.label1.Location = new System.Drawing.Point(35, 19);
this.label1.Name = "label1";
this.label1.Size = new System.Drawing.Size(76, 13);
this.label1.TabIndex = 0;
this.label1.Text = "Enter value n: ";
//
// txtInput
//
this.txtInput.Location = new System.Drawing.Point(123, 16);
this.txtInput.Name = "txtInput";
this.txtInput.Size = new System.Drawing.Size(100, 20);
this.txtInput.TabIndex = 1;
//
// btnCalculate
//
this.btnCalculate.Location = new System.Drawing.Point(81, 81);
this.btnCalculate.Name = "btnCalculate";
this.btnCalculate.Size = new System.Drawing.Size(75, 23);
this.btnCalculate.TabIndex = 2;
this.btnCalculate.Text = "Calculate";
this.btnCalculate.UseVisualStyleBackColor = true;
this.btnCalculate.Click += new System.EventHandler(this.btnCalculate_Click);
//
// lbOutput
//
this.lbOutput.AutoSize = true;
this.lbOutput.Location = new System.Drawing.Point(94, 52);
this.lbOutput.Name = "lbOutput";
this.lbOutput.Size = new System.Drawing.Size(0, 13);
this.lbOutput.TabIndex = 3;
//
// NumberSeries
//
this.AutoScaleDimensions = new System.Drawing.SizeF(6F, 13F);
this.AutoScaleMode = System.Windows.Forms.AutoScaleMode.Font;
this.ClientSize = new System.Drawing.Size(256, 139);
this.Controls.Add(this.lbOutput);
this.Controls.Add(this.btnCalculate);
this.Controls.Add(this.txtInput);
this.Controls.Add(this.label1);
this.Name = "NumberSeries";
this.Text = "NumberSeries";
this.ResumeLayout(false);
this.PerformLayout();

}

#endregion

private System.Windows.Forms.Label label1;
private System.Windows.Forms.TextBox txtInput;
private System.Windows.Forms.Button btnCalculate;
private System.Windows.Forms.Label lbOutput;
}
}

Output: