Problems with calculator

[ichabod801]

You don't need to avoid negative figures turning into double operators. Let that happen, and then use replace on any double operators: text = text.replace(' - - ', ' - -'). But that may get tricky with double spaces cropping up.

I would normally approach this with regular expressions. Assuming this is homework and you can't use regular expressions, I would do one loop over the input string. For each character, if it's a number character, store it in a sub-string and build that sub-string character by character. When you get to an operator, append the number and then the operator into your list, and reset the sub-string. If you get an operator after an operator (or an operator at the beginning) you know that's a negative number, and you can put that in the sub string.