Check if TextBox input is a decimal number or not - C#

Question

My Goal: I want textbox to accept the decimal numbers like 123.45 or 0.45 or 1004.72. If the user types in letters like a or b or c, the program should display a message alerting the user to input only numbers.

My Problem: My code only checks for numbers like 1003 or 567 or 1. It does not check for decimal numbers like 123.45 or 0.45. How do I make my text box check for decimal numbers? Following is my code:

namespace Error_Testing
{

    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private void textBox1_TextChanged(object sender, EventArgs e)
        {
            string tString = textBox1.Text;
            if (tString.Trim() == "") return;
            for (int i = 0; i < tString.Length; i++)
            {
                if (!char.IsNumber(tString[i]))
                {
                    MessageBox.Show("Please enter a valid number");
                    return;
                }
            }
            //If it get's here it's a valid number
        }
    } 
}

I am a newbie and Thanks for your help in advance. :)

For one.. you aren't handling the '.' character. What happens when they enter this into the textbox? — Jon La Marr, Aug 26 '13 at 17:14
Are you trying to write you own check or are you OK with using a built in one? This is trivial in .NET with `decimal.TryParse` or `double.TryParse`. — cadrell0, Aug 26 '13 at 17:17
@JonLaMarr: If I enter 123. in textbox, a dialogue box appears on the screen: "Please enter a valid number". This means that the textbox is not checking for decimal numbers. — Smith, Aug 26 '13 at 17:17
@cadrell0: Yes, I am okay with the built in one or whichever is easier. However, I don't know how to do it since this is one of my first few attempts at c# coding. — Smith, Aug 26 '13 at 17:18
@cadrell0: Yes, I just saw NewHire's answer and its working. Thanks for help. — Smith, Aug 26 '13 at 17:20

score 23 · Accepted Answer · answered Aug 26 '13 at 17:15

23

use Decimal.TryParse to check if the string entered is decimal or not.

decimal d;
if(decimal.TryParse(textBox1.Text, out d))
{
    //valid 
}
else
{
    //invalid
    MessageBox.Show("Please enter a valid number");
    return;
}

answered Aug 26 '13 at 17:15

user2711965

1,795
2
14
34

For integers, use int.TryParse() – Rob van der Veer Aug 26 '13 at 17:17
@NewHire: It works! Thanks for helping. I will mark is as Answer soon. Thanks again. – Smith Aug 26 '13 at 17:21
@Smith, you are welcome, For parsing any number should always look for `TryParse` family methods, provided with different types. e.g. int.TryParse, DateTime.TryParse etc. – user2711965 Aug 26 '13 at 17:22

score 0 · Answer 2 · answered Jun 28 '15 at 05:40

0

decimal.Tryparse returns true for string containing "," character and for example string like "0,12" returns true.

answered Jun 28 '15 at 05:40

arun

1

Some countries use the "." as decimal separator and other countries use the "," as decimal separator. You can change this by changing your culture. See this answer for more information [stackoverflow answer](http://stackoverflow.com/questions/9160059/set-up-dot-instead-of-comma-in-numeric-values) – Erik Mar 29 '17 at 15:42

score 0 · Answer 3 · answered Oct 16 '17 at 06:26

private void txtrate_TextChanged_1(object sender, EventArgs e)
        {
            double parsedValue;
            decimal d;
            // That Check the Value Double or Not
            if (!double.TryParse(txtrate.Text, out parsedValue))
            {
                //Then Check The Value Decimal or double Becouse The Retailler Software Tack A decimal or double value
                if (decimal.TryParse(txtrate.Text, out d) || double.TryParse(txtrate.Text, out parsedValue))
                {
                    purchase();
                }
                else
                {
                    //otherwise focus on agin TextBox With Value 0
                    txtrate.Focus();                  
                    txtrate.Text = "0";                   
                }


            }
            else
            {
                // that function will be used for calculation Like 
                purchase();
                /*  if (txtqty.Text != "" && txtrate.Text != "")
                  {
                      double rate = Convert.ToDouble(txtrate.Text);
                      double Qty = Convert.ToDouble(txtqty.Text);
                      amt = rate * Qty;
                  }*/

            }`enter code here`
        }

Check if TextBox input is a decimal number or not - C#

3 Answers3

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