Hand-made stacks, queues and lists in C++

From Data Structures (Universidad de Alcalá, fall 2026). Lab assignment 1: load a BMP image, put every pixel into hand-written structures (stack, queue, row lists), process it and write it back out, all without std::vector or std::list.

#Design

Six small classes: Pixel (one node: red, green, blue and a next pointer), StackDS, QueueDS, RowListDS, ImageListDS and Core. main only creates Core and calls run().

void StackDS::push(const Pixel& p) {
    Pixel* n = new Pixel(p);
    n->next = top_;
    top_ = n;
    ++size_;
}

StackDS::~StackDS() {           // free every node: no leaks
    while (!isEmpty()) pop();
}

#Things worth remembering

• Rule of three. If a class owns raw pointers, write the destructor, and either write or delete the copy constructor and copy assignment. Otherwise two objects free the same nodes.
• Reading a stack without destroying it. Pop everything into a helper stack, use the values, then push them back. The original keeps its size and its top.
• Pixel order matters. A stack gives you the pixels reversed (LIFO); a queue keeps the file order (FIFO).
• BMP row padding. Each row is padded to a multiple of 4 bytes. The teacher's library computed the padding before reading the width, which broke images whose width isn't a multiple of 4. I found and fixed it by comparing the output pixel by pixel.

#Verification

• The round trip (image → stack → image_test.bmp) is identical to the original, pixel by pixel.
• 0 memory leaks (checked with leaks/valgrind) and 0 warnings with -Wall -Wextra.