//=========================================================================
// 分析后读取一个标记
//=========================================================================
private Token GetToken()
{
Token token = null;
// 忽略空白字符
while (HasChar && char.IsWhiteSpace(CurrentChar))
{
MoveNext();
}
if (!HasChar)
{
return(null);
}
if (CurrentChar == '(') // 左括号
{
token = new LP();
}
else if (CurrentChar == ')') // 右括号
{
token = new RP();
}
else if (IsOper(CurrentChar)) // 操作符
{
token = new Oper(CurrentChar);
}
else if (char.IsDigit(CurrentChar)) // 数字
{
bool dotFound = false;
StringBuilder buf = new StringBuilder();
do
{
char c = CurrentChar;
if (dotFound && c == '.')
{
throw new Exception("无效的数字!");
}
buf.Append(c);
MoveNext();
} while (HasChar && (char.IsDigit(CurrentChar) || CurrentChar == '.'));
MovePrev(); // 回溯一次
token = new Number(Convert.ToDouble(buf.ToString()));
}
else
{
throw new Exception("表达式中含有无效字符:'" + CurrentChar + "'!");
}
MoveNext();
return(token);
}