STL — Standard Template Library

#include <iostream>
#include <vector>
#include <algorithm>
using namespace std;

int main() {
    // vector — dynamic size array
    vector<int> v = {5, 2, 8, 1, 9, 3};
    vector<string> names;

    // Add elements
    names.push_back("Rahul");
    names.push_back("Priya");
    names.push_back("Amit");

    // Size
    cout << "Size: " << v.size() << endl;  // 6

    // Access
    cout << v[0]      << endl;  // 5
    cout << v.at(1)   << endl;  // 2 — bounds check
    cout << v.front() << endl;  // 5 — first
    cout << v.back()  << endl;  // 3 — last

    // Remove last
    v.pop_back();
    cout << "After pop: " << v.size() << endl;  // 5

    // Sort
    sort(v.begin(), v.end());
    for (auto x : v) cout << x << " ";
    cout << endl;  // 1 2 5 8 9

    // Range-based for
    for (const auto &name : names) {
        cout << name << endl;
    }

    return 0;
}

#include <iostream>
#include <map>
using namespace std;

int main() {
    // map<key_type, value_type>
    map<string, int> marks;

    // Insert
    marks["Rahul"] = 85;
    marks["Priya"] = 92;
    marks["Amit"]  = 78;

    // Access
    cout << marks["Rahul"] << endl;  // 85

    // Iterate — automatically sorted by key
    for (auto &pair : marks) {
        cout << pair.first << ": " << pair.second << endl;
    }
    // Amit: 78
    // Priya: 92
    // Rahul: 85

    // Check key exists
    if (marks.count("Priya")) {
        cout << "Priya found!" << endl;
    }

    // Erase
    marks.erase("Amit");
    cout << "Size: " << marks.size() << endl;  // 2

    return 0;
}

#include <set>
#include <stack>
#include <queue>

// set — unique values, auto sorted
set<int> s = {5, 2, 8, 2, 1, 5};  // duplicates remove!
for (int x : s) cout << x << " ";
cout << endl;  // 1 2 5 8

// stack — LIFO (Last In First Out)
stack<int> stk;
stk.push(1);  stk.push(2);  stk.push(3);
cout << stk.top() << endl;  // 3
stk.pop();
cout << stk.top() << endl;  // 2

// queue — FIFO (First In First Out)
queue<string> q;
q.push("Rahul"); q.push("Priya"); q.push("Amit");
cout << q.front() << endl;  // Rahul
q.pop();
cout << q.front() << endl;  // Priya