Iterators | Notion

🔷 1. What is an Iterator?

Iterator ek pointer-like object hota hai jo STL containers (like vector, set, map, etc.) ke elements pe traverse (chalne) ke liye use hota hai.

💡 Socho ki iterator ek smart pointer hai — jo begin() se end() tak chalta hai.

🔹 2. Syntax of Iterator

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vector<int>::iterator it;

Yahaan:

vector<int> = container type
::iterator = us container ka iterator type
it = iterator variable

🔹 3. Basic Use with Vector

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

int main() {
    vector<int> v = {10, 20, 30};

    vector<int>::iterator it;
    for(it = v.begin(); it != v.end(); it++) {
        cout << *it << " ";  // *it means value at that iterator (just like pointer)
    }
    return 0;
}

🔷 4. Important Iterator Functions

Function	Meaning
`begin()`	First element ka iterator
`end()`	Last element ke baad ka iterator (not the last element itself)
`rbegin()`	Reverse begin (last element se start hota hai)
`rend()`	Reverse end (first se pehle ka position)
`it++`	Move to next element
`it--`	Move to previous element
`*it`	Iterator ke current position ka value

🔷 5. Range-Based For Loop (Recommended)

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for(auto it : v) {
    cout << it << " ";
}

⚡ Ye internally iterator ka hi use karta hai — easy and clean syntax!