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Regex to check whether entered string is numeric or not in Asp.net C#,VB

Check string is numeric or not in asp.net C# VBIntroduction: In this article i am going to share the code trick to check whether entered string is numeric/number or not in asp.net using regular expression in both C# and VB languages.

Description: While working on asp.net project i got the requirement to test whether the entered string is number or not? The solution is very easy and i am going to share two solutions for this with all so that other developers can implement it in their project easily whenever required.


Check the first solution by visiting the link "Check whether a string is numeric or not in Asp.net" and second you will get in this article using regular expression.


Implementation: Let's create a demo small web application to test the string is number or not.

Asp.Net C# Section
  • In the <Form> tag of the design page(default.aspx) design the page as:

 <div>
    <fieldset style="width:200px;">
    <legend>Check String is numeric or not</legend>
    <center>
<table>
<tr>
<td>
    <asp:TextBox ID="txtTest" runat="server"></asp:TextBox>
    </td>
</tr>
<tr>
<td>
     <asp:Button ID="btnTest" runat="server" onclick="btnTest_Click"
            Text="Test String" /><br />
        <asp:Label ID="lblStatus" runat="server"></asp:Label>
    </td>
</tr>
</table>
</center>
    </fieldset>
    </div>

  • In the code behind file(default.aspx.cs) write the code as:

protected void btnTest_Click(object sender, EventArgs e)
    {
        if (IsNumeric(txtTest.Text.Trim()))
        {
            lblStatus.Text = txtTest.Text + " is Numeric";
            lblStatus.ForeColor = System.Drawing.Color.Green;
        }
        else
        {
            lblStatus.Text = txtTest.Text + " is not Numeric";
            lblStatus.ForeColor = System.Drawing.Color.Green;
        }
    }

System.Text.RegularExpressions.Regex reg = new System.Text.RegularExpressions.Regex(@"^[0-9]+$");

    public bool IsNumeric(String str)
    {
        try
        {
            if (string.IsNullOrEmpty(str))
            {               
                return false;
            }
            if (!reg.IsMatch(str))
            {
                return false;
            }
        }
        catch (Exception ex)
        {
            lblStatus.Text = "Error occured : " + ex.Message.ToString();
            lblStatus.ForeColor = System.Drawing.Color.Red;
        }
        return false;
    }

Asp.Net VB section:
  • In the <Form> tag of the design page(default.aspx) design the page as:

<div>
    <fieldset style="width:200px;">
    <legend>Check String is numeric or not</legend>
    <center>
<table>
<tr>
<td>
    <asp:TextBox ID="txtTest" runat="server"></asp:TextBox>
    </td>
</tr>
<tr>
<td>
     <asp:Button ID="btnTest" runat="server" Text="Test String" /><br />
        <asp:Label ID="lblStatus" runat="server"></asp:Label>
    </td>
</tr>
</table>
</center>
    </fieldset>
    </div>

  • In the code behind file (default.aspx.vb) write the code as:

Protected Sub btnTest_Click(sender As Object, e As System.EventArgs) Handles btnTest.Click
        If IsNumeric(txtTest.Text.Trim()) Then
            lblStatus.Text = txtTest.Text + " is Numeric"
            lblStatus.ForeColor = System.Drawing.Color.Green
        Else
            lblStatus.Text = txtTest.Text + " is not Numeric"
            lblStatus.ForeColor = System.Drawing.Color.Green
        End If
    End Sub

Private reg As New System.Text.RegularExpressions.Regex("^[0-9]+$")

    Public Function IsNumeric(str As [String]) As Boolean
        Try
            If String.IsNullOrEmpty(str) Then
                Return False
            End If
            If Not reg.IsMatch(str) Then
                Return False
            End If
        Catch ex As Exception
            lblStatus.Text = "Error occured : " & ex.Message.ToString()
            lblStatus.ForeColor = System.Drawing.Color.Red
        End Try
        Return False
    End Function


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