利用%x直接輸出16進位制數，簡單模擬即可，水題

程式碼：

#include <cstdio>
#include <cstring>
#include <algorithm>
using namespace std;

const int N = 1000005;
char s[N];

int main() {
    while (gets(s) != NULL) {
        int len = strlen(s);
        for (int i = 0; i < len; i += 16) {
            printf("%04x: ", i);
            for (int j = i; j < i + 16; j += 2){
                if (j >= len) printf("     ");
                else if (j + 1 >= (i + 1) * 16 || (j + 1) >= len) printf("%02x   ", s[j]);
                else printf("%02x%02x ", s[j], s[j + 1]);
            }
            for (int j = len; j < len; j += 2) printf("     ");
            for (int j = i; j < i + 16 && j < len; j++) {
                if (s[j] >= 'a' && s[j] <= 'z') printf("%c", s[j] - 'a' + 'A');
                else if (s[j] >= 'A' && s[j] <= 'Z') printf("%c", s[j] - 'A' + 'a');
                else printf("%c", s[j]);
            }
            printf("\n");
        }
    }
    return 0;
}