private void GetNext()
{
SkipWhitespace();
char ch = GetNextChar();
if (Char.IsDigit(ch))
{
StringBuilder str = new StringBuilder();
while (Char.IsDigit(ch))
{
str.Append(ch);
ch = GetNextChar();
}
index--;
try
{
constant = op.Parse(str.ToString());
}
catch
{
throw new OverflowException();
}
current = State.number;
}
else if (ch == '+')
{
current = State.plus;
}
else if (ch == '-')
{
if (expression.Length >= index + 10 && expression.Substring(index, index + 10).Equals("2147483648"))
{
constant = op.Parse(expression.Substring(index - 1, index + 10));
index += 10;
current = State.number;
}
else
{
current = State.minus;
}
}
else if (ch == '*')
{
current = State.asterisk;
}
else if (ch == '/')
{
current = State.slash;
}
else if (ch == '(')
{
current = State.lparen;
}
else if (ch == ')')
{
current = State.rparen;
}
else if (ch == 'x' || ch == 'y' || ch == 'z')
{
current = State.variable;
variable = ch;
}
else
{
if (expression.Length >= index + 2 && expression.Substring(index - 1, index + 2).Equals("abs"))
{
index += 2;
current = State.abs;
}
else if (expression.Length >= index + 5 && expression.Substring(index - 1, index + 5).Equals("square"))
{
index += 5;
current = State.square;
}
else if (expression.Length >= index + 2 && expression.Substring(index - 1, index + 2).Equals("mod"))
{
index += 2;
current = State.mod;
}
else if (!Char.IsWhiteSpace(ch))
{
throw new ParsingException("unexpected char: \"" + ch + "\" at index: " + (index - 1));
}
}
SkipWhitespace();
}