Key point
One habit
Never trust a C++ project that only ran once in your IDE. Build it from the terminal, run small tests, then debug with tools when it fails.
Your HackIndia repo should let another builder clone it, compile it, and check sample cases without guessing.
Compile locally
For a small project, one clear compile command is enough. Keep it in your README and test it on your own laptop before submitting.
Use warnings while building. They catch many bugs before your program runs.
Example