How to ignore '\n' while using key detections C++

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C++14

i am using m menu function in c++ console app. it selects on pressing enter key but it i call it back to back then it select first option automatically. how can i clear input buffer so that '\n' is ignored.
for example i have 2 menus

<----main menu----->
Create
Display
Delete
Exit

<---- create SubMenu----->
Manager
Labour
Back

in this menus, if i select create option then manager is selected atomatically.

What I have tried:

i tried

<pre lang="c++">
cin.ignore();
cin.ignore(/*length*/,'\n');
cin.ignore('\0');
cin.sync();

but nothing worked.