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How to check whether a 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 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 have created a function for this purpose and  i am going to share the solution with all so that developers can implement it in their project easily whenever required.


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;
        }
    }

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

Note: Above created function "IsNumeric" consider only integer numbers e.g. 123 to be numeric. But if you want above function also consider the string like 123.5 i.e. the values with decimals to be numeric then you can replace the following two lines
int num;
if (int.TryParse(str, out num))

with these two lines:

double num;
if (double.TryParse(str, out num))

Now it will also consider the string with decimals e.g. 45.8 etc to be numeric.

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

    Public Function IsNumeric(str As [String]) As Boolean
        Try
            If Not String.IsNullOrEmpty(str) Then
                Dim num As Integer
                If Integer.TryParse(str, num) Then
                    Return True
                End If
            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

Note: Above created function "IsNumeric" consider only integer numbers e.g. 123 to be numeric. But if you want above function also consider the string like 123.5 i.e. the values with decimals to be numeric then you can replace the following two lines
Dim num As Integer
If Integer.TryParse(str, num) Then

 with these two lines:

Dim num As Double
If Double.TryParse(str, num) Then

Now it will also consider the string with decimals e.g. 45.8 etc to be numeric.

Now over to you:
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2 comments

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Anonymous
admin
April 25, 2014 ×

Does your function consider 3.14 to be numeric?

Reply
avatar
April 26, 2014 ×

No, i will only consider integer numbers to be numeric..if you want 3.14 to be considered numeric then you can use double num;
if (double.TryParse(str, out num)) instead of
int num;
if (int.TryParse(str, out num))

Reply
avatar

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