Simple input and button with pure C + Win32 API

gui-example.c

#include <windows.h>

#define ID_EDITBOX    1001
#define ID_BUTTON_OK  1002

void DrawCustomButton(LPDRAWITEMSTRUCT lpDrawItem) {

    COLORREF bgColor = RGB(255, 165, 0);     // orange
    COLORREF textColor = RGB(128, 128, 128);   // grey

    HBRUSH hBrush = CreateSolidBrush(bgColor);
    FillRect(lpDrawItem->hDC, &lpDrawItem->rcItem, hBrush);
    DeleteObject(hBrush);

    HFONT hFont = CreateFontW(
        20, 0, 0, 0,
        FW_NORMAL, FALSE, FALSE, FALSE,
        DEFAULT_CHARSET,
        OUT_DEFAULT_PRECIS,
        CLIP_DEFAULT_PRECIS,
        DEFAULT_QUALITY,
        DEFAULT_PITCH | FF_SWISS,
        L"Helvetica"
    );
    HFONT hOldFont = SelectObject(lpDrawItem->hDC, hFont);

    SetTextColor(lpDrawItem->hDC, textColor);
    SetBkMode(lpDrawItem->hDC, TRANSPARENT);

    wchar_t text[256];
    GetWindowTextW(lpDrawItem->hwndItem, text, 256);

    RECT rcText = lpDrawItem->rcItem;
    DrawTextW(lpDrawItem->hDC, text, -1, &rcText, DT_CENTER | DT_VCENTER | DT_SINGLELINE);

    SelectObject(lpDrawItem->hDC, hOldFont);
    DeleteObject(hFont);

    if (lpDrawItem->itemState & ODS_FOCUS) {
        DrawFocusRect(lpDrawItem->hDC, &lpDrawItem->rcItem);
    }
}

LRESULT CALLBACK WindowProc(HWND hwnd, UINT uMsg, WPARAM wParam, LPARAM lParam) {
    static HFONT hFontButton = NULL;
    switch(uMsg) {
        case WM_CREATE:
        {
            LPCREATESTRUCTW pcs = (LPCREATESTRUCTW)lParam;

            HWND hEdit = CreateWindowExW(
                0,
                L"EDIT",
                L"",
                WS_CHILD | WS_VISIBLE | WS_BORDER | ES_AUTOHSCROLL,
                10, 10, 200, 25,
                hwnd,
                (HMENU)ID_EDITBOX,
                pcs->hInstance,
                NULL
            );

            HWND hButton = CreateWindowExW(
                0,
                L"BUTTON",
                L"Hello!",
                WS_TABSTOP | WS_VISIBLE | WS_CHILD | BS_PUSHBUTTON | BS_OWNERDRAW,
                220, 10, 100, 25,
                hwnd,
                (HMENU)ID_BUTTON_OK,
                pcs->hInstance,
                NULL
            );

            hFontButton = CreateFontW(
                20, 0, 0, 0,
                FW_NORMAL, FALSE, FALSE, FALSE,
                DEFAULT_CHARSET,
                OUT_DEFAULT_PRECIS,
                CLIP_DEFAULT_PRECIS,
                DEFAULT_QUALITY,
                DEFAULT_PITCH | FF_SWISS,
                L"Arial"
            );
            
            SendMessageW(hButton, WM_SETFONT, (WPARAM)hFontButton, TRUE);
        }
        break;

        case WM_DRAWITEM:
        {
            LPDRAWITEMSTRUCT lpDrawItem = (LPDRAWITEMSTRUCT)lParam;
            if (lpDrawItem->CtlID == ID_BUTTON_OK) {
                DrawCustomButton(lpDrawItem);
                return TRUE;
            }
        }
        break;

        case WM_DESTROY:
            PostQuitMessage(0);
            break;

        default:
            return DefWindowProcW(hwnd, uMsg, wParam, lParam);
    }
    return 0;
}

int WINAPI wWinMain(HINSTANCE hInstance, HINSTANCE hPrevInstance, PWSTR pCmdLine, int nCmdShow) {
    const wchar_t CLASS_NAME[] = L"MyWindowClass";

    WNDCLASSW wc = {0};
    wc.lpfnWndProc   = WindowProc;
    wc.hInstance     = hInstance;
    wc.lpszClassName = CLASS_NAME;
    wc.hCursor       = LoadCursorW(NULL, IDC_ARROW);
    wc.hbrBackground = (HBRUSH)(COLOR_WINDOW+1);

    if (!RegisterClassW(&wc)) {
        return 0;
    }

    HWND hwnd = CreateWindowExW(
        0,
        CLASS_NAME,
        L"Window + input + button example",
        WS_OVERLAPPEDWINDOW,
        CW_USEDEFAULT, CW_USEDEFAULT, 400, 150,
        NULL,
        NULL,
        hInstance,
        NULL
    );

    if (hwnd == NULL) {
        return 0;
    }

    ShowWindow(hwnd, nCmdShow);

    MSG msg = {0};
    
    while (GetMessageW(&msg, NULL, 0, 0)) {
        TranslateMessage(&msg);
        DispatchMessageW(&msg);
    }

    return 0;
}

Instructions

You can compile this code using Visual Studio, but I compiled it using MSYS2 MingW64's GCC for Windows:

1. Download and install MSYS2: https://www.msys2.org/#installation
2. On Windows Start Bar, open MSYS2 MingW64
3. then execute this command to install GCC:

pacman -Syu && pacman -S base-devel

(yes, if you don't know, MSYS2 uses Arch Linux package manager Pacman)
sometimes it asks you that to complete the update the terminal should be closed. Just open it again.

4. then check to see if GCC is installed correctly with gcc --version:
   

5. I saved this code in my Desktop, so I have to cd into it:

cd /c/Users/<your user here>/Desktop/

Now you can compile this code above:

gcc gui-example.c -o gui-example.exe -municode -mwindows

then just double click the gui-example.exe: