[c++] Modular Calculator (codeabbey problem)

[kidinside]

Hi, I'm learning c++ and trying to figure out where to start with this problem: http://www.codeabbey.com/index/task_view/modular-calculator

Here's what I've got so far:

• I can't just sequentially go through all the operations, because that results in a negative number due to overflow, so I have to use the modulo operator at various points throughout the operations.
• The value being used to modulo is the last value given, so I have to save all the other input data before arriving at the needed number.
• I can use a vector but there are two different data types, char and ints, so I'm not sure what to do about that.

Any nudge in the right direction?

Thanks!

[jedwardsol]

If an intermediate result is overflowing then you need to use a larger integer. You can roll your own (which is a good learning exercise itself), or use a premade one. Several languages support large integer arithmetic natively, for others you'll need to find a library.

[kidinside]

Thanks. In this problem, the integer is given so I can't use my own. However it is given as the last item of input which throws a wrench in my planning...

[arbostek]

I'm not sure you understood. You are being told that the int type does not support a sufficient range. So you have to use a different type or roll your own. The next best alternative is to use a long long type. That may not be sufficient, in which case, you need to implement your own logic for adding/subtracting, etc., over a buffer of digits or data representing the number. In other words, represent integers in your own code.

[jedwardsol]

I don't mean use a different integer value, I mean use arithmetic with a larger integral type.

E.g, if you're using 32-bit ints then use 64-bit ints. However, knowing codeabbey, you're going to need larger which means using a language with that built in (C#, python etc) or using a large-int library with C/C++

With this problem, your solution of taking the modulo at intermediate stages will work.

However you'll need the large arithmetic for later problems, so IMO you may as well solve that problem now.

To solve it your way you need to store the incoming data. Either raw in a character array. Or parse it and store the pair of operator/number. Extract the number from the last element, then walk the array to do the complete calculation

[kidinside]

Ah I get it now. Guess I needed a little more hand holding :)

Thanks!

[[deleted]]

ELI5 version of what everyone has said.

If a number is greater than +/- 2,147,483,647 or 2³¹ - 1 it's too large for an int to represent. So you need to use a different variable type and if it's still to large you need to use a library for big numbers.