I started to write a pseudo-code answer but the question is simply too broad. You need to use strstr, you need to use strcpy, you need to write a loop. Explaining how to do these things in detail is the task of the string handling chapter in your C book. I voted to close it as "too generic", please try to ask specific questions rather than questions of the nature "how do I write this whole program".

Maybe we could assume that the asker has knowledge of C but doesn't know of any algorithm to accomplish the task. An answer could then first explain a suitable algorithm (relying only on tools available in C) and then simply present an implementation in C without much explanation. That's at least the way I thought about it, when editing the question.

Trilarion‭ I don't think such an answer will be of particular high quality. This is best answered by studying the string handling chapter in a C book, then make an attempt to solve the problem and ask specific questions about the code when stuck.

@Lundin You mean there is no complete solution to the whole problem possible within reasonable space in an answer or it would not be instructive to read about the whole solution in one go? I mostly take home that the problem might still be too broad and needs to be divided into smaller pieces.