discuss about project

That doesn't narrow it down much. Are you having a problem, don't know where to start?

@hamza. While you may have an idea of your design, what you posted has many missing parts.

For example you lead with "code in a data structure" which sounds odd to me. I usually put my c++ code into the files that are to be compiled. So maybe it's just the wrong words.

Next you note it's "online" so what does this look like? Say a browser pointing to your servers running this c++ code? Wouldn't that be a lot of work where you really should have a high level design such as "web and SQL services along with my code to make an online voting system"? It's doubtful you would create all this in just c++.

@Hazma_23, "i want to write code in data structure using c++."
*This statement is straight forward enough.

Data Structures Using C++, 2nd Ed., (945 Pages)
By D.S. Malik, Department of Computer Science - University of Houston
http://www2.cs.uh.edu/~rizk/teaching/cosc2430/books/DataStructuresUsingC.pdf

@Hazma_23, "my topic is online voting system."
*This topic is security sensitive and complex.

*rproffitt is correct: You'll need to learn more than just programming in C++. Getting started in C++ is fine for a proto-type voting system. The other languages will be Information Systems Dependent: Platform, Storage/Server, Cryptographic Algorithms & Block Chains, Communication Method(s), Etcetera. Completely depends on what you are going to be working with. Your major work will be above and beyond simply programming in a language to get a Voting System to work.

*A decent note on language integration problems, especially problematic with a voting system.
Java Tip 17: Integrating Java with C++
By Bill Foote, JavaWorld
https://www.javaworld.com/article/2077513/learn-java/java-tip-17--integrating-java-with-c--.html

*As far as getting working code or snippets, I won't be posting anything. It's not the same thing as Opinion Polling where counting anonymous data (ISP IP ID aside) isn't a security issue and an analog push button counter works fine.

*Online Voting or Electronic Voting is still considered in it's infancy stage and not 100% trustworthy (for whatever reason), hence not everyone is willing to adopt or use it. Some brave countries have used Online/Electronic Voting for public elections and some Universities have also used it for their internal elections.

Some reference ideas:

Ben Lynn Notes (Stanford University)
Covering: Cryptography, Time Complexity, Probability, One-way Functions, PRNGs, Hardcore Bits, Blum-Micali, Session Keys, PRFs, GGM Construction, PRPs, Secure Function Evaluation, Yao’s SFE, BGW SFE, Oblivious Transfer, Factoring, Zero-Knowledge, Broadcast, Voting, and Additional Notes.
https://crypto.stanford.edu/pbc/notes/crypto/voting.html

Development of Online Voting System using Minutiae based Algorithm
By Talib A. Divan, and Veena A. Gulhane (International Journal of Scientific & Engineering Research)
Covering: EVM, Fingerprint, FAR, FRR, Minutiae based algorithm, Template, Voting system
https://pdfs.semanticscholar.org/2fd1/f46922e1212666b585af102a0fcc725aeebd.pdf

Detailed Implementation of E-Voting System for on Duty Persons using RSA Algorithm with Kerberos Concept
By Ms. Tanzila Afrin, and Prof.K.J.Satao (International Journal of Innovative Research in Computer and Communication Engineering)
Covering: Encryption, Decryption, RSA, public key, E-voting, KDC, TGS
http://www.rroij.com/open-access/detailed-implementation-ofevoting-system-for-on-duty-persons-usingrsa-algorithm-with-kerberos-concept-.php?aid=43591

*This is enough to get your feet wet and figure out where to start. The stuff I've listed aren't the only resources and ideas available. Only thing left is rproffitt's ... "web and SQL services along with [his] code to make an online voting system". An AI Online Voting System where Cortana makes suggestions as to whom you should vote for, Siruis to criticize you for your vote, and Amazon Echo to guess whom you wanted to vote for and randomly send your voting information to someone on your client list. :) Have fun everyone.