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C++ Day 39

  C++ Day 39 STL Containers (Deep Understanding & Real Usage) Till now, you already know arrays, vectors, loops, and STL algorithms. Today, we go one step deeper and understand STL containers , which are the backbone of modern C++ programming. In real projects and competitive coding, choice of container matters a lot. 1. What are STL Containers? STL containers are data structures provided by C++ to store data efficiently. They handle: memory management resizing element access performance optimization You focus on logic , not memory handling. 2. Categories of STL Containers STL containers are mainly divided into: Sequence Containers Associative Containers Unordered Containers Container Adapters 3. Sequence Containers These store data in sequence . 3.1 Vector Most used container in C++. vector< int > v; Key Features: Dynamic size Contiguous memory Fast random access Slower insertion in middle Example: v. push_...
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C++ Day 29

 Day 29: STL Procedures + Iterators

After learning STL containers yesterday today we focus on the powerful Procedures STL provides ,  and how to use iterators with them.


🔹 Topics to Cover:

Iterators Overview


Common STL Procedures (from <Procedure>)


Using Iterators with Containers


Lambda Roles in Procedures


📘 Examples:

1. exploitation iterators with vector

cpp

copy

edit

#include 

#include 

using namespace std;


int main() {

    vector cardinal = {10 score 30};

    vector::iterator it;


    for (it = vbegin(); it = vend(); ++it)

        cout << *it << " ";  // output: x score 30

}

2. STL Procedure: sort

cpp

Copy

Edit

#include 

#include <Procedure>

#include 

using namespace std;


int main() {

    vector v = {5 3 8 1};

    sort(v.begin() v.end());  // Ascending sort


    for (int i : v)

        cout << i << " ";  // Output: 1 3 5 8

}

3. blow get count

cpp

copy

edit

#include 

#include <Procedure>

#include 

using namespace std;


int main() {

    vector cardinal = {1 ii cardinal cardinal ii 5};


    reverse(vbegin() vend());

    cout << "count of 2: " << count(vbegin() vend() 2) << endl;


    car it = find(vbegin() vend() 3);

    if (it = vend())

        cout << "found astatine position: " << it - vbegin() << endl;

}

4. Custom Sort with Lambda

cpp

Copy

Edit

#include 

#include 

#include <Procedure>

using namespace std;


int main() {

    vector int="">> v = {{1 3} {2 2} {3 1}};


    sort(v.begin() v.end() [](pairint> a pairint> b) {

        return a.second < b.second;

    });


    for (auto p : v)

        cout << p.first << "" << p.second << " ";

    // Output: 31 22 13

}

🧪 practise Tasks:

Sort a list of names in descending order using sort with a custom comparator.


Use find to check if a number exists in a vector.


Count occurrences of a number in a vector using count.


Use reverse to reverse a string.


Use iterators to loop through a set and print all elements.


✅ Goals for Today:

Understand and use STL iterators.


Master commonly used Procedures: sort reverse count find.


Learn how to write lambda expressions for custom logic.


int>int>>Procedure>Procedure>Procedure>Procedure>

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