DSA: Stack – Introduction & Implementations – C++

[sharma-anahita]

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Description 📜

This PR adds a new Stack topic under the DSA domain.

The contribution includes:

• Introduction to Stack and its core concepts
• Stack implementations in C++ using:
  • Array
  • Linked List
  • STL (std::stack)
• A roadmap of standard stack problems to be added in future contributions

This improves the completeness of the DSA section by covering a core linear data structure with both conceptual and practical implementations.

Fixes #8974

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Type of change 📝

• Documentation (Content Creation in the form of codes or tutorials)

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Domain of Contribution 📊

• DSA
• C/CPP

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Checklist ✅

• I follow Contributing Guidelines & Code of conduct of this project.
• I have performed a self-review of my own code or work.
• I have commented my code, particularly in hard-to-understand areas.
• My changes generates no new warnings.
• I'm GWOC'25 contributor

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Screenshots / Gif (Optional) 📸

Not applicable (documentation and code-based contribution).

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