**Has to be in C++

3.4 Converting base representation. Write a function convertbase which converts a number, represented as a string in one base, to a new string representing that number in a new base. You may assume that the number can be stored in an int without overflow. string convertbase (const string& numstr, const int frombase, const int tobase) The character to represent a digit with value digitvalue is the ASCII character digitvalue+'0' The values of frombase and tobase will always be in the range 2 to 200 incsive