Data Structures in C/C++

Circular Queue

A circular buffer reuses freed array positions instead of shifting elements after every removal.

What is Circular Queue?

A circular buffer reuses freed array positions instead of shifting elements after every removal.

Implement first-in, first-out processing.

Important points

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

C and C++ code examples

Run code →

main.c

#include <stdio.h>

typedef struct {
    int data[4];
    int head;
    int size;
} Queue;

int push(Queue *queue, int value) {
    if (queue->size == 4) return 0;
    int tail = (queue->head + queue->size) % 4;
    queue->data[tail] = value;
    ++queue->size;
    return 1;
}

int pop(Queue *queue, int *value) {
    if (queue->size == 0) return 0;
    *value = queue->data[queue->head];
    queue->head = (queue->head + 1) % 4;
    --queue->size;
    return 1;
}

int main(void) {
    Queue queue = {{0}, 0, 0};
    int value;
    push(&queue, 7);
    push(&queue, 9);
    pop(&queue, &value);
    printf("%d\n", value);
}

Expected output

C++

Run code →

main.cpp

#include <iostream>
#include <queue>

int main() {
    std::queue<int> values;
    values.push(7);
    values.push(9);
    std::cout << values.front() << '\n';
    values.pop();
}

Expected output

C and C++ comparison

The C queue tracks head and size and wraps indices with modulo. std::queue provides a container adapter with front, push, and pop.

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.