*Has to be in C++

3.3 Adding big integers Write a function that adds two non-negative integers represented as strings, returning the result as a string. The function must use the following signature: string add (const string& num1, const string& num2) The values numi and num2 can represent arbitrarily long integers, so all the calculations must be done without using integer types (except for calculating each digit.) There is no need to check for or deal with strings that do not represent non negative integers