Message from C, C++ talks
1) Don't use compile time arrays, they will fill your heap space up.
2) don't read a full line at once, because it will make you do the parsing twice
3) You can do the parsing recursively because you know that if there is something after the second operand, you have a second equation.
do something like this:
a + b
if after b, you have another operation, you evaluate
a + (b + c)
that way, you don't even have to store the numbers, meaning that you will be less likely to fuck up and you won't even have to use the std::vecto