Dynamic Array and std::vector in C and C++

What is Dynamic Array and std::vector?

A dynamic array keeps a logical size separate from allocated capacity and reallocates geometrically.

Important points

State the invariants before implementing operations.
Handle empty, full, and allocation-failure cases.
Measure time complexity and memory ownership together.

See how it works

Press push_back repeatedly. When the array is full it allocates a block twice as big and copies everything across.

C and C++ code examples

C

Run code →

main.c

#include <stdio.h>
#include <stdlib.h>

int main(void) {
    size_t size = 0, capacity = 2;
    int *values = malloc(capacity * sizeof *values);
    if (!values) return 1;
    for (int value = 1; value <= 5; ++value) {
        if (size == capacity) {
            capacity *= 2;
            int *grown = realloc(values, capacity * sizeof *values);
            if (!grown) {
                free(values);
                return 1;
            }
            values = grown;
        }
        values[size++] = value * value;
    }
    printf("size=%zu capacity=%zu last=%d\n",
           size, capacity, values[size - 1]);
    free(values);
}

Result of running the code

size=5 capacity=8 last=25

C++

Run code →

main.cpp

#include <iostream>
#include <vector>

int main() {
    std::vector<int> values;
    for (int value = 1; value <= 5; ++value) {
        values.push_back(value * value);
    }
    std::cout << "size=" << values.size()
              << " last=" << values.back() << '\n';
}

Result of running the code

size=5 last=25

C and C++ comparison

The C version explicitly checks realloc and updates capacity. std::vector packages the same growth strategy with automatic destruction, iterators, and exception safety.

C

Structures and operations are usually separate and allocation is explicit.

C++

Classes and containers can preserve invariants and manage resources automatically.

Practice exercises

Run both versions, then modify them to observe the different language guarantees.

Add empty and capacity-boundary tests.
Implement cleanup and verify no leaks remain.
Compare operation complexity with a standard container.

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