Question

Using only stdio.h, string.h and stdlib.h libraries how would I go about implementing this?

I’m quite new to programming so please bear with me!

Answer 1

1. Allocate a new char array of the same length as your string. Convince yourself that this is enough space. Don’t forget the NUL.
2. Loop through the string, copying to the new string only those characters that are alphanumeric. You can’t do this portably without also including <ctype.h> and using a function/macro from that header, unless you’re going to enumerate all characters that you consider alphanumeric.
3. Again, don’t forget the NUL.