mouse clickable backspace button in c#

Question

I wanted to make a backspace button for my calculator app in windows form the problem is it deletes the character to the right of the cursor, not the left what can I do?

 private void DeleteTextValue()
    {
        //if we don't have any value to delete, return 
        if (this.UserInput.Text.Length < this.UserInput.SelectionStart + 1)
            return;

        //remember cursor location
        var selectionStart = this.UserInput.SelectionStart;

        //delete the char to the right of the cursor
        this.UserInput.Text = this.UserInput.Text.Remove(this.UserInput.Text.Length-1, 1);

        //restore the cursor location
        this.UserInput.SelectionStart = selectionStart;

        //unhighlight the text
        this.UserInput.SelectionStart = 0 ;
    }

Answer 1

Try this, I used substring instead of remove.

private void DeleteTextValue()
    {
        //if we don't have any value to delete, return 
        if (this.UserInput.Text.Length < this.UserInput.SelectionStart + 1)
            return;

        //remember cursor location
        var selectionStart = this.UserInput.SelectionStart;

        //delete the char to the right of the cursor
        //this.UserInput.Text = this.UserInput.Text.Remove(this.UserInput.Text.Length - 1, 1);
                    
        if (UserInput.SelectedText.Length > 0)
        {
            UserInput.Text = this.UserInput.Text.Substring(0, this.UserInput.SelectionStart) + "" + this.UserInput.Text.Substring(this.UserInput.SelectionStart + this.UserInput.SelectionLength);
            selectionStart = selectionStart - this.UserInput.SelectionLength; 
        }
        else
        {
            UserInput.Text = this.UserInput.Text.Substring(0, this.UserInput.SelectionStart - 1) + "" + this.UserInput.Text.Substring(this.UserInput.SelectionStart);
            selectionStart = selectionStart - 1;
        }
        UserInput.Focus();
        //restore the cursor location
        this.UserInput.SelectionStart = selectionStart;

        //unhighlight the text
         this.UserInput.SelectionLength= 0;
    }