/// <summary>
/// Appends character depending on pressed button.
/// </summary>
private void AppendCharacter(object sender, RoutedEventArgs e)
{
if (operationExecutor.State == ExecutorState.OperatorGot)
{
inputValidator.ClearInput();
operationExecutor.State = ExecutorState.SecondOperandInput;
}
if (operationExecutor.State == ExecutorState.ResultCalculated ||
operationExecutor.State == ExecutorState.Error)
{
inputValidator.ClearInput();
SetSecondaryOutput("");
operationExecutor.Clear();
}
string newText = inputValidator.Validate((sender as Button).Content.ToString());
SetMainOutput(newText);
}