adding char * as unsigned int

[LHernandez]

Please HELP:

This is the declaration of a function that adds together two unsigned integer numbers represented as strings:

void Add(const char * s1, const char * s2, char * result);

The function returns the result in a caller-supplied buffer
assuming that it is always big enough.

E.g. char result[50];

Add(“1273”, “16”, result);

Will return “1289” in the result buffer.

How can I write an implementation of the function in C++ w/o
using atoi(), itoa() or other standard functions for conversion.