How can I find the last character of a textbox text?

Question

I am a beginner in C#. I am making a web calculator like Microsoft Desktop calculator with the help of asp.net. But I'm stuck at one place. My code for Plus, minus, multiply or div is like:

protected void btnPlus_Click(object sender, EventArgs e)
{
    if (txtBox1.Text.EndsWith("+"))
    {
        txtBox1.Text = txtBox1.Text;
    }
    else
    {
        txtBox1.Text = txtBox1.Text + "+";
        ViewState["Operation"] = "+";
    }
}

But I want to check this condition for all operations like minus, multiply and divide. I don't want Plus, Minus, Multiply or Div signs appear in the textbox.

Answer 1

You can store all your operators in a string constant and check if the last character is contained in that string:

private const string OPERATORS = "+-/*";
protected void btnPlus_Click(object sender, EventArgs e)
{
    if (string.IsNullOrEmpty(txtBox1.Text) || // check if string is empty
        OPERATORS.Contains(txtBox1.Text.Last())) // or if last character is a operator
    {
        txtBox1.Text = txtBox1.Text;
    }
    else
    {
        txtBox1.Text = txtBox1.Text + "+";
        ViewState["Operation"] = "+";
    }
}

Answer 2

You can do something like the following:

1. Extract last character
2. Based on the character assign operator to the view state
3. If it is any operator then remove them from the textbox

4. Finally do the operation

    if (txtBox1.Text != "")
           {
               char last_char = txtBox1.Text[txtBox1.Text.Length - 1];
               switch (last_char)
               {
                   case '+':
                       ViewState["Operation"] = "+";
                       txtBox1.Text.Remove(txtBox1.Text.Length - 1);
                       break;
                   case '-':
                       ViewState["Operation"] = "-";
                       txtBox1.Text.Remove(txtBox1.Text.Length - 1);
                       break;
                   // do the same for all operators
                   default:
   
                       break;
               }
           }