要在C++中實現貪吃蛇游戲的圖形界面設計，可以使用圖形庫如SFML（Simple and Fast Multimedia Library）或者Qt等。下面是一個使用SFML庫實現貪吃蛇游戲的簡單示例：

#include <SFML/Graphics.hpp>
#include <vector>

const int blockSize = 20;
const int width = 800;
const int height = 600;

struct SnakeSegment {
    int x, y;
};

int main() {
    sf::RenderWindow window(sf::VideoMode(width, height), "Snake Game");

    std::vector<SnakeSegment> snake;
    snake.push_back({width / 2, height / 2});

    sf::RectangleShape food(sf::Vector2f(blockSize, blockSize));
    food.setFillColor(sf::Color::Red);
    food.setPosition(100, 100);

    sf::Clock clock;
    float timer = 0;
    float delay = 0.1;

    while (window.isOpen()) {
        float deltaTime = clock.restart().asSeconds();
        timer += deltaTime;

        sf::Event event;
        while (window.pollEvent(event)) {
            if (event.type == sf::Event::Closed) {
                window.close();
            }
        }

        if (sf::Keyboard::isKeyPressed(sf::Keyboard::Left)) {
            // Move left
        }
        else if (sf::Keyboard::isKeyPressed(sf::Keyboard::Right)) {
            // Move right
        }
        else if (sf::Keyboard::isKeyPressed(sf::Keyboard::Up)) {
            // Move up
        }
        else if (sf::Keyboard::isKeyPressed(sf::Keyboard::Down)) {
            // Move down
        }

        window.clear();

        // Draw snake
        for (SnakeSegment segment : snake) {
            sf::RectangleShape segmentShape(sf::Vector2f(blockSize, blockSize));
            segmentShape.setFillColor(sf::Color::Green);
            segmentShape.setPosition(segment.x, segment.y);
            window.draw(segmentShape);
        }

        // Draw food
        window.draw(food);

        window.display();
    }

    return 0;
}

在這個示例中，我們使用SFML庫創建了一個窗口，繪制了貪吃蛇和食物的矩形形狀，并添加了基本的鍵盤控制邏輯。您可以根據需要自定義游戲邏輯和圖形界面設計。希望這個示例對您有所幫助！