Share portion

I found out that making this program is very easy in terms of math and everything. I made this to practice my skills in C++. If you are a noob at C++ and want to do something like this, here is an example!

Question

I didn't know where to post this (which board), so I decided to share it AND include my question. I want to make a program that levels the player up at specific points of XP. Say, the player hits 50 XP and levels up. How would I make it so that they level up at 100 XP after I reset the XP from the previous level up?