算法如下：
struct code_val scanner(char *buf);
{
	static int i=0;
	struct code_val t={'\0',"NUL"};
	char token[WORDLEN]="";
	while(buf[i]= =' ') i++;
	if(buf[i] >= 'a' && buf[i] <= 'Z')
	{
		while(buf[i]>='a' && buf[i]<='Z' || buf[i]>='0' && buf[i]='9')
			concat(token,buf[i++]);
		t.code=reserve(token);
		if(t.code= ='i') strcpy(t.val,token);
		return t;
		if(buf[i]>='0' && buf[i]='9')
		{
			while(buf[i]>='0' && buf[i]='9')
				concat(token,buf[i++]);
			if(buf[i]= ='.') 
			{ 
				concat(token,buf[i++]);
				while(buf[i]>='0' && buf[i]='9')
					concat(token,buf[i++]);
				t.code='y';
			}
		}
		else
			t.code='x';
		strcpy(t.val,token);
		return t;
	}
	if(buf[i]= ='.')
	{ 
		concat(token,buf[i++]);
		if(buf[i]>='0' && buf[i]='9')
		{
			while(buf[i]>='0' && buf[i]='9')
				concat(token,buf[i++]);
			t.code='y';
			strcpy(t.val,token);
			return t;
		}
		else {
			cout<<"error word>"<<token<<endl;
			exit(0);
		}
	}
	switch(buf[i]) {
	case ',':
		t.code=',';break;
	case ';':
        t.code=';';break;
    case '(':
        t.code='(';break;
    case ')':
        t.code=')';break;
    case '=':
        t.code='=';break;
    case '+':
		if(buf[++i]= ='+')
			t.code='$';
		else 
		{
			t.code='+';i--;
		}
		break;
    case '*':
        t.code='*';break;
    case '#':
        t.code='#';break;
    default:
        cout<<"error char>"<<buf[i]<<endl;
        exit(0);
	}
	i++;
	return t;
}