void AddOperatorToExpr(char token, int index)
{
// An operator can follow a number or a symbol, thus:
AddOperandToExpr();
exprList.Add(CalcToken.Operator(token, index));
}
// -----------------------------------------
// --- Methods for multicharacter tokens ---
// -----------------------------------------
void UpdateLastOperator(char c)
{
int lastIdx = exprList.Count - 1;
var last = exprList[lastIdx];
string newOp = last.Value + c;
exprList[lastIdx] = CalcToken.Operator(newOp, last.OriginIndex);
}