//后序表达式求值
private string PostfixEval(string postExp)
{
Stack<double> result = new Stack<double>();
double x, y;
for (int i = 0; i <= postExp.Length - 1; i++)
{
Operator op = new Operator(postExp[i]);
if (IsDigit(postExp[i]))
{
string operand = "";
while ((i <= postExp.Length - 1) && IsDigit(postExp[i]))
{
operand += postExp[i];
i++;
}
i--;
result.Push(Convert.ToDouble(operand));
continue;
}
if (postExp[i] == ' ') continue;
if (op.isSingle)
{
y = result.Pop();
result.Push(op.Parse(y));
}
else
{
y = result.Pop();
x = result.Pop();
result.Push(op.Parse(x, y));
}
}
return Convert.ToString(result.Peek());
}
