> "...would let the program know..."
Ah. No, the program doesn't "know" anything. If you call a function and do nothing with the return value, then the return value is lost. The program knows nothing that you don't explicitly tell it, and if you don't explicitly tell it to do something about the return value then it'll do nothing. There is absolutely no intelligence there, and the program doesn't know what you mean.
Assuming you're referring to the strcmp before the while (strcmp), the first is effectively a no-operation, because it doesn't modify the strings passed in and nothing happens to the return value.