Congratulations on considering to write at OpenGenus IQ 
for C++ language.
This is a small list of topics that you can write about C++ 
Programming Language.
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For using this task list, check out this guide.
Following is the list of topics:
Variable and Fundamental types
- Variables (assigned to @mqshaikh8)
- Fundamental data types (assigned to @siddharthgusain)
- auto (assigned to @Harshita)
- decltype (assigned to @Harshita)
- Type casting (assigned to @Harshita)
- How to take input in C++?
- Output in C++ (assigned to @chetali19)
- Steps in C++ program compilation (assigned)
User defined types
- Classes and Objects (assigned to @Robotjelly123)
- Constructors (assigned to @Harshita)
- Scope (assigned to @Robotjelly123)
- Struct (assigned to @chetali19)
- Namespace (assigned to @Harshita)
- Inheritance (assigned to @Robotjelly123)
- Enumeration (assigned to @Harshita)
- Operator overloading (assigned to @Robotjelly123)
Flow control
- flow control (assigned to @shreyagupta30)
- If else (assigned to @Harshita)
- while (assigned to @Harshita)
- do while (assigned to @Harshita)
- for loop (assigned to @Harshita)
- switch case (assigned to @Harshita)
Functions
- Functions (done by @Harshita)
- Types of User-defined Functions (assigned to @Robotjelly123)
- Function overloading (assigned to @Harshita)
- Default argument (assigned to @Harshita)
- Storage class (assigned to @shreyarastogi)
Inheritance
- Single inheritance (assigned to @chetali19)
- Multilevel inheritance (assigned to @imskr)
- Hierarchical inheritance (assigned to @Harshita)
- Hybrid inheritance (assigned to @chetali19)
- Multipath inheritance (assigned to @chetali19)
- Multiple inheritance (assigned to @shreyarastogi)
- Function overriding (assigned to @Harshita)
- Friend function (assigned to @shreyagupta30)
- Virtual function (assigned to @Harshita)
- Templates (assigned to @xamfy)
Pointers
- Pointers (assigned to @shreyagupta30)
- Function pointers (assigned to @chetali19)
- Array + Multi-dimensional array (assigned to @tarique)
Memory management
- new (assigned to @Harshita)
- malloc
- calloc
- delete (assigned to @Harshita)
- malloc vs calloc vs realloc (done by @Harshita)
- Static memory management
- Dynamic memory management (assigned to @Jeson)
C++ libraries
- unique_ptr (done by @goxul)
- shared_ptr (assigned)
- weak_ptr (assigned)
- Container (assigned to @Harshita)
- Vector (assigned to @shreyagupta30)
- List (assigned to @aryabharat)
- Set (assigned to @Robotjelly123)
- Map (assigned to @Robotjelly123)
- Multimap (assigned to @Robotjelly123)
- Unordered Map (assigned to @Robotjelly123)
Standard Template Library
- queue (assigned to @r0uxt1)
- priority queue (assigned to @r0uxt1)
- stack (assigned to @piyush26c)
- deque (assigned to @r0uxt1)
- functors (assigned to @Harshita)
- iterators (assigned to @Harshita)
- pair (assigned to @r0uxt1)
- Commonly used utilities
- Standard Template library
Concurrency
- Processes and Fork (assigned to @goxul)
- Zombie process
- Orphan process
- Threads (done by @vineet)
- Synchronization (assigned)
- Concurrency (assigned)
- Locks
- Mutex lock
- Critical section
- Reader writer problem (assigned to @Robotjelly123)
Design patterns in C++
- Observer pattern (assigned to @Harshita)
- Command Pattern
- Singleton Pattern (assigned to @Harshita)
- Builder Pattern (assigned to @Harshita)
- Factory Pattern (assigned to @Harshita)
- Abstract Factory Pattern (assigned to @Harshita)
- Null Object Pattern (assigned to @Harshita)
- Strategy design pattern
- Adapter pattern
- State pattern
- Design pattern classification (assigned to @Harshita)
- Classification:
- Creational
- Structural
- Behavioral
- Concurrency
Others
- Exception handling
- Recursion (done by @Harshita)
- Object slicing
- [Add your topic]