Vector Basics in C++

Basic Vector Operations in C++.

BeginnerSTL Containers ProgramsExample 1 of 10

vector-basics.cpp

1#include <iostream>
2#include <vector>
3using namespace std;
4
5int main() {
6    // Create vector
7    vector<int> vec;
8    
9    // Add elements
10    vec.push_back(10);
11    vec.push_back(20);
12    vec.push_back(30);
13    vec.push_back(40);
14    vec.push_back(50);
15    
16    cout << "Vector elements: ";
17    for (int i = 0; i < vec.size(); i++) {
18        cout << vec[i] << " ";
19    }
20    cout << endl;
21    
22    // Access elements
23    cout << "First element: " << vec.front() << endl;
24    cout << "Last element: " << vec.back() << endl;
25    cout << "Element at index 2: " << vec.at(2) << endl;
26    
27    // Size and capacity
28    cout << "Size: " << vec.size() << endl;
29    cout << "Capacity: " << vec.capacity() << endl;
30    
31    // Initialize vector with values
32    vector<int> vec2 = {1, 2, 3, 4, 5};
33    cout << "\nVector 2: ";
34    for (int num : vec2) {
35        cout << num << " ";
36    }
37    cout << endl;
38    
39    // Remove last element
40    vec.pop_back();
41    cout << "\nAfter pop_back: ";
42    for (int num : vec) {
43        cout << num << " ";
44    }
45    cout << endl;
46    
47    return 0;
48}

Output

Vector elements: 10 20 30 40 50
First element: 10
Last element: 50
Element at index 2: 30
Size: 5
Capacity: 8

Vector 2: 1 2 3 4 5

After pop_back: 10 20 30 40

What's going on

The program demonstrates basic vector operations:

Creating and initializing vectors

Adding elements with push_back()

Accessing elements (front, back, at, index)

Getting size and capacity

Removing elements with pop_back()

Vectors are the most commonly used STL container.

Header Files Used

1.#include <iostream>

Provides cout and cin for input/output operations.

2.#include <vector>

Provides vector container class.

Understanding Vectors

Vector Concept

Dynamic array that resizes automatically

Elements stored contiguously in memory

Random access (like arrays)

Efficient insertion/deletion at end

Key Features

Automatic memory management

Can grow and shrink dynamically

Cache-friendly (contiguous memory)

Part of STL (Standard Template Library)

Creating Vectors

Empty Vector

vector<int> vec;

Initialized Vector

vector<int> vec2 = {1, 2, 3, 4, 5};

How it works

Template syntax: vector<dataType>

Can hold any data type

Initially empty (size 0)

Can initialize with values

Adding Elements

push_back()

vec.push_back(10);

vec.push_back(20);

vec.push_back(30);

How it works

Adds element to end of vector

Automatically resizes if needed

O(1) amortized time complexity

Most efficient way to add elements

Accessing Elements

Methods

vec[i]: array-like access (no bounds check)

vec.at(i): access with bounds check (throws exception)

vec.front(): first element

vec.back(): last element

Example

vec.front() // Returns 10

vec.back() // Returns 30

vec.at(2) // Returns 30 (with bounds check)

vec[1] // Returns 20 (no bounds check)

Size and Capacity

Size

vec.size() // Number of elements

Capacity

vec.capacity() // Allocated memory size

How it works

Size: actual number of elements

Capacity: memory allocated (usually larger)

Vector pre-allocates extra memory

Resizes when capacity exceeded

Removing Elements

pop_back()

vec.pop_back(); // Removes last element

How it works

Removes element from end

O(1) time complexity

Reduces size (not capacity)

Efficient operation

When to Use Vectors

Best For

Dynamic arrays (size changes)

Random access requirements

Frequent insertion/deletion at end

General-purpose container

Most common STL container

Example Scenarios

Reading unknown number of elements

Dynamic data structures

Arrays that need to grow

General data storage

Important Considerations

Memory Layout

Elements stored contiguously

Cache-friendly (good performance)

Like arrays but dynamic

Performance

push_back(): O(1) amortized

pop_back(): O(1)

Random access: O(1)

Insert/delete in middle: O(n)

Automatic Management

Memory allocated automatically

Resizes when needed

No manual memory management

Exception-safe

return 0;

This ends the program successfully.

NextVector Operations