public static double get_value(IGetVariable p, string s)
{
if (char.IsLetter(s, 0))
{
return(p.GetVariable(s));
}
else
{
return(double.Parse(s));
}
}
public double GetValue(IGetVariable gv)
{
if (user)
{
return(val);
}
else
{
return(Expr.Evaluate(expr, gv));
}
}
public static double Evaluate(string s, IGetVariable p)
{
string[] toks = lex(s);
Stack <string> stk = new Stack <string>();
Stack <double> stk2 = new Stack <double>();
for (int i = 0; i < toks.Length; i++)
{
string t = toks[i];
string tnext = null;
string tprev = null;
if ((i + 1) < toks.Length)
{
tnext = toks[i + 1];
}
if (i > 0)
{
tprev = toks[i - 1];
}
if (t == "(")
{
stk.Push(t);
}
else if (t == ")")
{
while (true)
{
if (stk.Count == 0)
{
throw new Exception("Unbalanced paren");
}
string q = (string)stk.Pop();
if (q == "(")
{
break;
}
else
{
do_op(stk2, q);
}
}
}
else if (is_operand(t))
{
stk2.Push(get_value(p, t));
}
else if (
(t == "-") &&
(tnext != null) &&
(is_operand(tnext)) &&
(
is_operator(tprev) ||
(
(stk.Count == 0) &&
(stk2.Count == 0)
)
)
)
{
stk2.Push(-get_value(p, tnext));
i++;
}
else
{
Debug.Assert(is_operator(t));
do
{
if (stk.Count == 0)
{
stk.Push(t);
break;
}
else if (((string)stk.Peek()) == "(")
{
stk.Push(t);
break;
}
else if (op_precedence(t) > op_precedence((string)stk.Peek()))
{
stk.Push(t);
break;
}
else
{
do_op(stk2, (string)stk.Pop());
}
} while (true);
}
}
while (stk.Count > 0)
{
do_op(stk2, (string)stk.Pop());
}
double result = (double)stk2.Pop();
if (stk2.Count > 0)
{
throw new Exception("Stack should be empty at the end of the expression");
}
return(result);
}
