コード:

#include "DxLib.h"

void update(char *str, const char *s, int k)
{
    for (int i = 0; i < k; i++)
        str[i] = GetRand(9) + '0';
    for (int i = k; i < 8; i++)
        str[i] = s[i];
    str[8] = '\0';
}

int WINAPI WinMain(HINSTANCE, HINSTANCE, LPSTR, int)
{
    ChangeWindowMode(TRUE), DxLib_Init(), SetDrawScreen(DX_SCREEN_BACK);
    int y = 40, t = 0, k = 8;
    char str[9];
    unsigned c1 = GetColor(0, 255, 0), c2 = GetColor(0, 255, 255);
    while (!ScreenFlip() && !ProcessMessage() && !ClearDrawScreen()) {
        int t1 = t % 120 - 60;
        y = 40 + 0.1 * t1 * t1;
        DrawBox(300, y, 300 + 40, y + 30, c1, TRUE);
        if (t % 6 == 0) update(str, "12345678", k);
        if (k > 0 && t % 30 == 0) k--;
        DrawString(100, 100, str, c2);
        if (CheckHitKey(KEY_INPUT_ESCAPE)) k = 8;
        t++;
    }
    DxLib_End();
    return 0;
}  

コード:

#include <stdio.h>   // putchar, fflush
#include <stdlib.h>  // rand, srand
#include <time.h>    // time
#if defined(__GNUC__)
#include <unistd.h>  // usleep
#define SLEEP(msec)  usleep(msec * 1000)
#else
#include <windows.h> // Sleep
#define SLEEP(msec)  Sleep(msec)
#endif

#define N 8

void display(void)
{
    int i, j, k, a[N];
    srand(time(0));
    for (i = N; i > 0; i--) {
        for (j = 0; j < 6; j++) {
            putchar('\r');
            for (k = 0; k < i; k++) putchar(a[k] = rand() % 10 + '0');
            for (k = i; k < N; k++) putchar(a[k]);
            putchar('\a');
            fflush(stdout);
            SLEEP(100);
        }
    }
    putchar('\n');
}

int main(void)
{
    char buf[256];
    do {
        display();
        printf("once again? (y/n) ");
    } while (fgets(buf, sizeof buf, stdin) && buf[0] == 'y');
}