In this blog we will see how to test whether a given number entered in a textbox is a valid integer or an invalid integer.

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 Valid_or_Invalid_integer

{

public partial class Form1 : Form

{

public Form1()

{

InitializeComponent();

}

private void btn_valid_invalid_Click(object sender, EventArgs e)

{

int i;

bool isValidInteger = int.TryParse(textBox1.Text, out i);

if (!isValidInteger)

{

MessageBox.Show("Not a valid integer.Please enter once again!");

textBox1.Focus();

return;

}

else

{

MessageBox.Show("Valid integer");

textBox1.Focus();

}

}

}

}