Calculate TextBox Value like calculator calculation using C# in ASP.Net

Hi paulrajmca,

Use the below line to calculate like mathematical formula.

string output = new System.Data.DataTable().Compute(txtCalculate.Text.Trim(), null).ToString();

If you want to simply calculate like calculator then use the below.

C#

string[] decimalNumbers = txtCalculate.Text.Split('+', '-', '*', '/');
string[] operators = txtCalculate.Text.Split('0', '1', '2', '3', '4', '5', '6', '7', '8', '9', '.');

List<string> s = new List<string>();
foreach (var item in operators)
{
    if (!string.IsNullOrEmpty(item))
    {
        s.Add(item);
    }
}
decimal intSum = 0;
for (int i = 0; i < decimalNumbers.Length; i++)
{
    if (i == 0)
    {
        intSum = Convert.ToDecimal(decimalNumbers[i]);
    }
    if (i > 0)
    {
        string oprator = s[i - 1];
        switch (oprator)
        {
            case "+":
                intSum = intSum + Convert.ToDecimal(decimalNumbers[i]);
                break;
            case "-":
                intSum = intSum - Convert.ToDecimal(decimalNumbers[i]);
                break;
            case "*":
                intSum = intSum * Convert.ToDecimal(decimalNumbers[i]);
                break;
            case "/":
                intSum = intSum / Convert.ToDecimal(decimalNumbers[i]);
                break;
        }
    }
}
lblResult.Text = Math.Round(intSum, 2).ToString();