How to Make a Textbox That Only Accepts Numbers in C#

1. Make a Textbox That Only Accepts Numbers Using KeyPressEventArgs Class in C#
2. Make a Textbox That Only Accepts Numbers Using Regex.IsMatch() Method in C#
3. Make a Textbox That Only Accepts Numbers Using NumericUpDown Method

While making Windows Forms, some text fields only need a numeric value. For example, if we want to get the phone numbers from users then we will have to restrict our textbox to numeric values only.

In this article, we will focus on the methods that make a textbox that only accepts numbers.

Make a Textbox That Only Accepts Numbers Using KeyPressEventArgs Class in C#

KeyPressEventArgs is a C# class that specifies the character entered when a user presses a key. Its KeyChar property returns the character that the user typed. Here we have used the KeyPress event to limit our textbox to numeric values only.

The key code that performs this action is as follows:

!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && (e.KeyChar != '.');

Here e is a KeyPressEventArgs object that uses KeyChar property to fetch the entered key.

Example Code:

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 WindowsFormsApplication1 {
  public partial class Form1 : Form {
    public Form1() {
      InitializeComponent();
    }
    private void textBox1_KeyPress(object sender, KeyPressEventArgs e) {
      if (!char.IsControl(e.KeyChar) && !char.IsDigit(e.KeyChar) && (e.KeyChar != '.')) {
        e.Handled = true;
      }

      // only allow one decimal point
      if ((e.KeyChar == '.') && ((sender as TextBox).Text.IndexOf('.') > -1)) {
        e.Handled = true;
      }
    }
  }
}

Output:

//only allows numeric values in the textbox

Make a Textbox That Only Accepts Numbers Using Regex.IsMatch() Method in C#

In C# we can use regular expressions to check various patterns. A regular expression is a specific pattern to perform a specific action. RegularExpressions is a C# class that contains the definition for Regex.IsMatch() method. In C#, we have ^[0-9]+$ and ^\d+$ regular expressions to check if a string is a number.

The correct syntax to use this method is as follows:

Regex.IsMatch(StringName, @"Expression");

Example Code:

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 WindowsFormsApplication1 {
  public partial class Form1 : Form {
    public Form1() {
      InitializeComponent();
    }
    private void textBox1_TextChanged(object sender, EventArgs e) {
      if (System.Text.RegularExpressions.Regex.IsMatch(textBox1.Text, "  ^ [0-9]")) {
        textBox1.Text = "";
      }
    }
  }
}

Output:

//A textbox created that only accepts numbers.

Make a Textbox That Only Accepts Numbers Using NumericUpDown Method

NumericUpDown provides the user with an interface to enter a numeric value using up and down buttons given with the textbox. You can simply drag and drop a NumericUpDown from the Toolbox to create a textbox that only accepts numbers.

You can also create a NumericUpDown object dynamically. The code to generate a NumericUpDown is as follows:

private System.Windows.Forms.NumericUpDown numericUpDown;
this.numericUpDown = new System.Windows.Forms.NumericUpDown();

It has several properties which you can modify by opening the Properties Windows.

Output: