//扫描一个单元
public clsToken scan()
{
if (tokenstatus == false)//如果前面操作，没有误吞字符，那么读一个
{
while (readOneChar())
{
//吞掉空格和换行符，已经制表符，遇到普通字符退出
if (peek == ' ' || peek == '\t')
{
continue;
}
else if (peek == '\n')
{
line++;
}
else
{
break;
}
}
}
else//否则用被吞字符
{
peek = tokenchar;
tokenstatus = false;
}
// 判断是否为数字数字
if (isDigit(peek))
{
int v = 0;
do
{
v = v * 10 + peek - '0';
readOneChar();
} while (isDigit(peek));
if (isIdentifierStart(peek))
{
//如数字后跟着的是字符的话，说明这是一个错误的标识符，而不是数字
//不管他，还是先读//读完之后，构造时，告诉程序，，这是个错误的标识符
StringBuilder b = new StringBuilder(v + "");
do
{
b.Append(peek);
readOneChar();
} while (isIdentifierStart(peek) || isDigit(peek));
Fortokenchar();
String s = b.ToString();
clsWord w = new clsWord(s, Tag.error, line);
return(w);
}
else if (peek != '.')
{
Fortokenchar();
return(new clsNum(v, line));
}
float x = v; float d = 10;
for (; ;)
{
readOneChar();
if (!isDigit(peek))
{
Fortokenchar();
break;
}
x += (peek - '0') / d;
d = d * 10;
}
if (isIdentifierStart(peek))
{
//如数字后跟着的是字符的话，说明这是一个错误的标识符，而不是数字
//不管他，还是先读//读完之后，构造时，告诉程序，，这是个错误的标识符
string tmpc = x + "";
StringBuilder b = new StringBuilder(tmpc);
do
{
b.Append(peek);
readOneChar();
} while (isIdentifierStart(peek) || isDigit(peek));
Fortokenchar();
String s = b.ToString();
clsWord w = new clsWord(s, Tag.error, line);
return(w);
}
return(new clsRealNum(x, line));
}
// 判断保留字或标识符
if (isIdentifierStart(peek))
{
StringBuilder b = new StringBuilder();
do
{
b.Append(peek);
readOneChar();
} while (isIdentifierStart(peek) || isDigit(peek));
Fortokenchar();
String s = b.ToString();
clsWord w;
if (words.Contains(s))
{
w = (clsWord)words[s];
string x = w.lexeme;
int y = w.tag;
clsWord newW = new clsWord(x, y, line);
return(newW);
}
w = new clsWord(s, Tag.ID, line);
//先把用户标识符，也放在words表里面，后面再改
// words.Add(w.lexeme, w);
return(w);
}
string stmp = "";
stmp += peek;
// 判断界限符
if (symbol.Contains(stmp))
{
clsToken w = (clsToken)symbol[stmp];
int x = w.tag;
if (x == Tag.delimiter)
{
clsDelimiter d = (clsDelimiter)symbol[stmp];
clsDelimiter newD = new clsDelimiter(d.sign, x, line);
return(newD);
}
}
clsToken t = new clsToken(peek, line);
peek = ' ';
return(t);
}
//将保留字存入hash表
public void PutReservedWord(clsWord t)
{
words.Add(t.lexeme, t);
}