读入一个正整数n，把他的每位用该数字为颜色号，半径为20的实心圆表示。求c语言代码

以下是基于Windows.h的C语言代码实现：

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

#define RADIUS 20    // 圆的半径
#define WIDTH 800    // 窗口宽度
#define HEIGHT 600   // 窗口高度

LRESULT CALLBACK WndProc(HWND, UINT, WPARAM, LPARAM);   // 窗口过程函数声明

int WINAPI WinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, LPSTR lpCmdLine, int nCmdShow) {
    const char szClassName[] = "MyWindowClass";   // 窗口类名
    HWND hwnd;   // 窗口句柄
    MSG msg;     // Windows消息结构体

    // 注册窗口类
    WNDCLASS wndclass = { 0 };
    wndclass.lpfnWndProc = WndProc;
    wndclass.hInstance = hInstance;
    wndclass.hbrBackground = (HBRUSH)(COLOR_WINDOW);
    wndclass.lpszClassName = szClassName;
    RegisterClass(&wndclass);

    // 创建窗口
    hwnd = CreateWindow(szClassName, "Draw Circles", WS_OVERLAPPEDWINDOW, CW_USEDEFAULT, CW_USEDEFAULT, WIDTH, HEIGHT, NULL, NULL, hInstance, NULL);

    // 显示窗口
    ShowWindow(hwnd, nCmdShow);
    UpdateWindow(hwnd);

    // 消息循环
    while (GetMessage(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessage(&msg);
    }

    return msg.wParam;
}

LRESULT CALLBACK WndProc(HWND hwnd, UINT msg, WPARAM wParam, LPARAM lParam) {
    static int n;   // 正整数n
    static int digits[10];   // n的每位数字
    static int numDigits = 0;   // n的位数
    int x, y;   // 圆心坐标
    int i;      // 循环计数器
    PAINTSTRUCT ps;
    HDC hdc;

    switch (msg) {
        case WM_CREATE:
            // 弹出输入对话框，读入正整数n
            if (MessageBox(hwnd, "Please enter a positive integer:", "Input", MB_OKCANCEL) == IDOK) {
                char buf[10];
                if (GetWindowText(GetDlgItem(hwnd, IDOK), buf, 10)) {
                    n = atoi(buf);
                    // 分离n的每位数字
                    while (n > 0) {
                        digits[numDigits++] = n % 10;
                        n /= 10;
                    }
                }
            }
            break;
        case WM_PAINT:
            hdc = BeginPaint(hwnd, &ps);
            // 计算圆心坐标，绘制圆
            for (i = 0; i < numDigits; i++) {
                x = (i + 1) * WIDTH / (numDigits + 1);
                y = HEIGHT / 2;
                SelectObject(hdc, CreateSolidBrush(RGB(255 - digits[i] * 20, digits[i] * 20, 0)));   // 根据数字选择颜色
                Ellipse(hdc, x - RADIUS, y - RADIUS, x + RADIUS, y + RADIUS);
                DeleteObject(SelectObject(hdc, GetStockObject(WHITE_BRUSH)));
            }
            EndPaint(hwnd, &ps);
            break;
        case WM_DESTROY:
            PostQuitMessage(0);
            break;
        default:
            return DefWindowProc(hwnd, msg, wParam, lParam);
    }

    return 0;
}

运行程序后，会弹出一个输入对话框，输入正整数n后，程序会在窗口中绘制各个数字对应的圆形，如下图所示：