3. Write a function, void to_lower(char* s), that replaces all uppercase characters in the C-style string s with their lowercase equivalents. For example, Hello, World! becomes hello, world!. Do not use any standard library functions. A C-style string is a zero-terminated array of characters, so if you find a char with the value 0 you are at the end.

4. Write a function, char* strdup(const char*), that copies a C-style string into memory it allocates on the free store. Do not use any standard library functions.