/* nuklear - v1.00 - public domain */
static void
calculator(struct nk_context *ctx)
{
    struct nk_panel layout;
    if (nk_begin(ctx, &layout, "Calculator", nk_rect(10, 10, 180, 250),
        NK_WINDOW_BORDER|NK_WINDOW_NO_SCROLLBAR|NK_WINDOW_MOVABLE))
    {
        static int set = 0, prev = 0, op = 0;
        static const char numbers[] = "789456123";
        static const char ops[] = "+-*/";
        static double a = 0, b = 0;
        static double *current = &a;

        size_t i = 0;
        int solve = 0;
        {int len; char buffer[256];
        nk_layout_row_dynamic(ctx, 35, 1);
        len = snprintf(buffer, 256, "%.2f", *current);
        nk_edit_string(ctx, NK_EDIT_SIMPLE, buffer, &len, 255, nk_filter_float);
        buffer[len] = 0;
        *current = atof(buffer);}

        nk_layout_row_dynamic(ctx, 35, 4);
        for (i = 0; i < 16; ++i) {
            if (i >= 12 && i < 15) {
                if (i > 12) continue;
                if (nk_button_label(ctx, "C", NK_BUTTON_DEFAULT)) {
                    a = b = op = 0; current = &a; set = 0;
                } if (nk_button_label(ctx, "0", NK_BUTTON_DEFAULT)) {
                    *current = *current*10.0f; set = 0;
                }
                if (nk_button_label(ctx, "=", NK_BUTTON_DEFAULT)) {
                    solve = 1; prev = op; op = 0;
                }
            } else if (((i+1) % 4)) {
                if (nk_button_text(ctx, &numbers[(i/4)*3+i%4], 1, NK_BUTTON_DEFAULT)) {
                    *current = *current * 10.0f + numbers[(i/4)*3+i%4] - '0';
                    set = 0;
                }
            } else if (nk_button_text(ctx, &ops[i/4], 1, NK_BUTTON_DEFAULT)) {
                if (!set) {
                    if (current != &b) {
                        current = &b;
                    } else {
                        prev = op;
                        solve = 1;
                    }
                }
                op = ops[i/4];
                set = 1;
            }
        }
        if (solve) {
            if (prev == '+') a = a + b;
            if (prev == '-') a = a - b;
            if (prev == '*') a = a * b;
            if (prev == '/') a = a / b;
            current = &a;
            if (set) current = &b;
            b = 0; set = 0;
        }
    }
    nk_end(ctx);
}