public int Calculate(string expression)
{
Context context = new Context();
IList<IExpression> tree = new List<IExpression>();
//词法和语法分析
char[] elements = expression.ToCharArray();
foreach(char c in elements)
{
if ((c == '+') || (c == '-'))
tree.Add(new Operator(c));
else
tree.Add(new Operand((int)(c-48)));
}
//便利中间每个过程
foreach(IExpression exp in tree)
exp.Evaluate(context);
return context.Value;
}
public virtual void Evaluate(Context context)
{
context.Operator = op;
}
//根据操作符执行计算
public virtual void Evaluate(Context c)
{
switch(c.Operator)
{
case '\0': c.Value = num; break;
case '+': c.Value += num; break;
case '-': c.Value -= num; break;
}
}