// Internal
private void AddItem(ExpressionItem itm)
{
if (itm is Operand)
{
++_validationCounter;
}
else if (itm is Operation)
{
if (itm.IsUnary)
{
--_validationCounter;
if (_validationCounter < 0)
{
throw new InvalidExprException();
}
++_validationCounter;
}
else
{
_validationCounter -= 2;
if (_validationCounter < 0)
{
throw new InvalidExprException();
}
++_validationCounter;
}
}
_result.Add(itm);
}
private static Operation ReadOperator(StringReader reader, ExpressionItem prevItem)
{
char sign = (char)reader.Read();
var result = Operation.BySign[sign];
if (result == Operation.Substract)
{
if (prevItem is Divisor || prevItem == null) // to use negation after operator brackets are necessary
{
result = Operation.Negation;
}
}
return(result);
}
/// <summary>
/// Parse string expression to List of <code>ExpressionItems</code> in postfix notation.
/// </summary>
/// <returns>List of <code>ExpressionItems</code> in postfix notation</returns>
/// <exception cref="InvalidExprException"></exception>
/// <exception cref="InvalidBracketsException"></exception>
public List <ExpressionItem> GetPostfixNotation()
{
_result = new List <ExpressionItem>();
using (var reader = new StringReader(_expression))
{
int peek;
ExpressionItem previous = null;
while ((peek = reader.Peek()) > -1)
{
char next = (char)peek;
if (char.IsDigit(next))
{
if (previous is Operand)
{
throw new InvalidExprException("Unexpexted token.");
}
previous = ReadOperand(reader);
AddItem(previous);
}
else if (Operation.IsOperator(next))
{
var nextOp = ReadOperator(reader, previous);
while ((_evalStack.Count > 0) && (_evalStack.Peek().StackPriority > nextOp.Priority))
{
AddItem(_evalStack.Pop());
}
_evalStack.Push(nextOp);
previous = nextOp;
}
else if (Divisor.IsDivisor(next))
{
var bracket = ReadDivisor(reader);
previous = bracket;
if (bracket == Divisor.OpenBracket)
{
_evalStack.Push(bracket);
}
else if (bracket == Divisor.CloseBracket)
{
try
{
while (_evalStack.Peek() != Divisor.OpenBracket)
{
AddItem(_evalStack.Pop());
}
_evalStack.Pop();
}
catch (InvalidOperationException)
{
throw new InvalidBracketsException();
}
}
}
else if (char.IsWhiteSpace(next))
{
reader.Read();
}
else
{
throw new InvalidExprException("Unknown symbols detected.");
}
}
while (_evalStack.Count > 0)
{
var tmp = _evalStack.Pop();
if (!(tmp is Divisor))
{
AddItem(tmp);
}
else
{
throw new InvalidBracketsException();
}
}
if (_validationCounter != 1)
{
throw new InvalidExprException();
}
return(_result);
}
}