Aside from the answers already mentioning header guards, maybe post the code of your files, if they are not too big. There are many mistakes to make which aren't exactly intuitive to understand. For example, you don't want to implement functions in headers, except if they are declared
inline
(although that would result in a compile time error rather than a runtime bug). Note that especially for a beginner, it is beneficial to post your code on
CodeReview to improve your style. —
Aziuth 47 secs ago