We’re comparing C++ arrays vs C++ vectors (from STL).

1️⃣ Basic Definition

Feature	Array	Vector
Type	Built-in language type	STL container (`std::vector`)
Size	Fixed at compile-time or runtime (C-style)	Dynamic, grows/shrinks automatically
Memory	Contiguous memory	Contiguous memory internally, manages memory automatically
Header	None	`#include <vector>`
Syntax	`int arr[5];`	`std::vector<int> v;`

2️⃣ Memory & Size

Array:

int arr[5];  // size = 5, cannot change

Size is fixed
If you try arr[10] = 7; → Undefined behavior
Stack allocated (or static/global)

Vector:

#include <vector>
std::vector<int> v;
v.push_back(10);
v.push_back(20);

Size is dynamic
Automatically resizes when adding elements
Allocates memory on heap internally

3️⃣ Access Elements

Both use indexing:

arr[0]      // Array
v[0]        // Vector
v.at(0)     // Vector with bounds checking

v.at(i) throws exception if out of bounds → safer than array

4️⃣ Advantages & Disadvantages

Array

✅ Pros:

Very fast (no memory management overhead)
Simple, low-level, minimal footprint

❌ Cons:

Fixed size → cannot grow
No built-in functions (push, pop, insert)

Vector

✅ Pros:

Dynamic size → easy to use
Many helper functions: push_back(), pop_back(), size(), clear()
Safer with .at() bounds checking

❌ Cons:

Slight overhead for dynamic memory allocation
Slightly slower than raw arrays in tight loops

5️⃣ When to use which

Scenario	Recommendation
You know the size at compile-time & performance-critical	Array
You need dynamic size & convenience	Vector
Need STL algorithms (`sort`, `find`)	Vector (works seamlessly)

6️⃣ Example

#include <iostream>
#include <vector>
#include <algorithm>int main() {
    int arr[3] = {1, 2, 3};
    std::cout << "Array: ";
    for(int i = 0; i < 3; i++) std::cout << arr[i] << " ";
    std::cout << "\n";    std::vector<int> v = {1, 2, 3};
    v.push_back(4);             // Dynamic size
    std::sort(v.begin(), v.end()); // STL algorithms
    std::cout << "Vector: ";
    for(int x : v) std::cout << x << " ";
}

Output:

Array: 1 2 3 
Vector: 1 2 3 4

7️⃣ Key Takeaway

Array → Low-level, fixed size, very fast
Vector → Modern C++ choice, flexible, safer, integrates with STL

💡 Most useful in real-world C++ projects: std::vector, because almost always you need dynamic size and STL support. Arrays are mostly used for performance-critical or embedded scenarios.

3. C++ arrays vs C++ vectors (from STL).