How to Compare two columns on a gridview and display it in the third?

few column data comming  from database after binding grid few column are iput column then i willsave data to another database table

You do not show where the data is coming from. I assume there is a list (or something like a list) of classes with Amount1 and Amount2 as members. It can also have a member for the result of the comparison. Then when the list is loaded process it to do the comparisons.

you can use this

protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        TextBox txtAmount1 = (TextBox)e.Row.FindControl("txtAmount1");
        TextBox txtAmount2 = (TextBox)e.Row.FindControl("txtAmount2");
        Label lblAmount = (Label)e.Row.FindControl("lblAmount");

        // Assuming the amounts are decimal values
        if (decimal.TryParse(txtAmount1.Text, out decimal amount1) && decimal.TryParse(txtAmount2.Text, out decimal amount2))
        {
            // Compare the amounts and set the text of lblAmount
            lblAmount.Text = (amount1 > amount2) ? amount1.ToString() : amount2.ToString();
        }
        else
        {
            // Handle invalid input if needed
            lblAmount.Text = "Invalid input";
        }
    }
}

amount1 and amount 2 user will input 

To compare the values in the "Amount1" and "Amount2" columns of a GridView and display the greater amount in the "Greater Amount" column, you can achieve this by using the RowDataBound event in the code-behind file of your ASP.NET page. Here's

 

protected void GridViewExample_RowDataBound(object sender, GridViewRowEventArgs e)
{
    if (e.Row.RowType == DataControlRowType.DataRow)
    {
        // Access the textboxes and label within the row
        TextBox txtAmount1 = (TextBox)e.Row.FindControl("txtAmount1");
        TextBox txtAmount2 = (TextBox)e.Row.FindControl("txtAmount2");
        Label lblAmount = (Label)e.Row.FindControl("lblAmount");

        // Compare the values and set the label text
        decimal amount1 = decimal.Parse(txtAmount1.Text);
        decimal amount2 = decimal.Parse(txtAmount2.Text);
        lblAmount.Text = amount1 > amount2 ? amount1.ToString() : amount2.ToString();
    }
}