使用C语言编写钢琴小程序

1. 环境配置
2. 安装C语言开发环境，推荐使用gcc编译器。
3. 安装SDL库，SDL是一套跨平台的游戏开发库，可以方便的创建图形界面和音频效果。

4. 在代码中包含SDL库头文件以及链接SDL静态库或者动态库。

5. 构建程序框架

6. 创建一个窗口用于展示钢琴的键盘和播放音频。
7. 定义音符的频率和时长，将每个音符映射到对应的键盘上。

8. 监听键盘事件，根据用户的输入播放相应的音符。

9. 程序实现
   示例1：初始化SDL库，创建钢琴窗口

#include <stdio.h>
#include <SDL.h>

const int SCREEN_WIDTH = 800;
const int SCREEN_HEIGHT = 600;

int main(int argc, char *argv[]) {
    // 初始化SDL
    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO) < 0) {
        printf("SDL初始化失败！错误：%s\n", SDL_GetError());
        return 1;
    }

    // 创建窗口
    SDL_Window *window = SDL_CreateWindow("Piano",
                                          SDL_WINDOWPOS_UNDEFINED,
                                          SDL_WINDOWPOS_UNDEFINED,
                                          SCREEN_WIDTH,
                                          SCREEN_HEIGHT,
                                          SDL_WINDOW_SHOWN);

    if (window == NULL) {
        printf("窗口创建失败！错误：%s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }

    // 等待窗口关闭
    bool quit = false;
    while (!quit) {
        SDL_Event event;
        while (SDL_PollEvent(&event) != 0) {
            if (event.type == SDL_QUIT) {
                quit = true;
            }
        }
    }

    // 退出SDL
    SDL_DestroyWindow(window);
    SDL_Quit();
    return 0;
}

示例2：监听键盘事件，根据用户输入播放音效

#include <stdio.h>
#include <SDL.h>

const int SCREEN_WIDTH = 800;
const int SCREEN_HEIGHT = 600;

bool isKeyDown(SDL_Keycode key) {
    const Uint8 *state = SDL_GetKeyboardState(NULL);
    return state[SDL_GetScancodeFromKey(key)];
}

int main(int argc, char *argv[]) {
    // 初始化SDL
    if (SDL_Init(SDL_INIT_VIDEO | SDL_INIT_AUDIO) < 0) {
        printf("SDL初始化失败！错误：%s\n", SDL_GetError());
        return 1;
    }

    // 创建窗口
    SDL_Window *window = SDL_CreateWindow("Piano",
                                          SDL_WINDOWPOS_UNDEFINED,
                                          SDL_WINDOWPOS_UNDEFINED,
                                          SCREEN_WIDTH,
                                          SCREEN_HEIGHT,
                                          SDL_WINDOW_SHOWN);

    if (window == NULL) {
        printf("窗口创建失败！错误：%s\n", SDL_GetError());
        SDL_Quit();
        return 1;
    }

    // 初始化音频子系统
    if (SDL_AudioInit(NULL) != 0) {
        printf("音频子系统初始化失败！错误：%s\n", SDL_GetError());
        SDL_DestroyWindow(window);
        SDL_Quit();
        return 1;
    }

    // 音频参数
    SDL_AudioSpec want, have;
    SDL_memset(&want, 0, sizeof(want));
    want.freq = 48000;
    want.format = AUDIO_S16SYS;
    want.channels = 2;
    want.samples = 4096;
    want.callback = NULL;

    // 打开音频设备
    SDL_AudioDeviceID device = SDL_OpenAudioDevice(NULL, 0, &want, &have, 0);
    if (device == 0) {
        printf("音频设备打开失败！错误：%s\n", SDL_GetError());
        SDL_DestroyWindow(window);
        SDL_Quit();
        return 1;
    }

    // 提示音符按键
    printf("请按下以下按键来弹奏钢琴：\nq w e r t y u i o p\n");

    // 音效数据
    int notes[10] = {330, 349, 392, 440, 494, 523, 587, 659, 698, 784};
    bool isPlay[10] = {false};

    // 等待窗口关闭
    bool quit = false;
    while (!quit) {
        SDL_Event event;
        while (SDL_PollEvent(&event) != 0) {
            if (event.type == SDL_QUIT) {
                quit = true;
            }
        }

        // 播放对应的音符
        if (isKeyDown(SDLK_q) && !isPlay[0]) {
            isPlay[0] = true;
            SDL_QueueAudio(device, &notes[0], sizeof(int));
        }

        if (isKeyDown(SDLK_w) && !isPlay[1]) {
            isPlay[1] = true;
            SDL_QueueAudio(device, &notes[1], sizeof(int));
        }

        if (isKeyDown(SDLK_e) && !isPlay[2]) {
            isPlay[2] = true;
            SDL_QueueAudio(device, &notes[2], sizeof(int));
        }

        if (isKeyDown(SDLK_r) && !isPlay[3]) {
            isPlay[3] = true;
            SDL_QueueAudio(device, &notes[3], sizeof(int));
        }

        if (isKeyDown(SDLK_t) && !isPlay[4]) {
            isPlay[4] = true;
            SDL_QueueAudio(device, &notes[4], sizeof(int));
        }

        if (isKeyDown(SDLK_y) && !isPlay[5]) {
            isPlay[5] = true;
            SDL_QueueAudio(device, &notes[5], sizeof(int));
        }

        if (isKeyDown(SDLK_u) && !isPlay[6]) {
            isPlay[6] = true;
            SDL_QueueAudio(device, &notes[6], sizeof(int));
        }

        if (isKeyDown(SDLK_i) && !isPlay[7]) {
            isPlay[7] = true;
            SDL_QueueAudio(device, &notes[7], sizeof(int));
        }

        if (isKeyDown(SDLK_o) && !isPlay[8]) {
            isPlay[8] = true;
            SDL_QueueAudio(device, &notes[8], sizeof(int));
        }

        if (isKeyDown(SDLK_p) && !isPlay[9]) {
            isPlay[9] = true;
            SDL_QueueAudio(device, &notes[9], sizeof(int));
        }

        // 监听音效结束事件，重置按键状态
        SDL_Delay(10);  // 避免CPU资源占用过高
        int queued = SDL_GetQueuedAudioSize(device);
        if (queued == 0) {
            for (int i = 0; i < 10; i++) {
                isPlay[i] = false;
            }
        }
    }

    // 关闭音频设备
    SDL_CloseAudioDevice(device);
    SDL_AudioQuit();

    // 退出SDL
    SDL_DestroyWindow(window);
    SDL_Quit();
    return 0;
}