#include <stdlib.h>
#include <stdio.h>
#include <string.h>
#include <ctype.h>

int main(int argc, char *argv[]) {
        char text[] = "aoai 1skkfd 34kdwn 99";
        size_t len = strlen(text);

        char digits[10];
        memset(digits, 0, 10);

        printf("Digits: ");
        for (size_t i = 0; i < len; ++i) {
                char c = text[i];
                if (isdigit(c)) {
                        digits[c - '0'] = 1;
                        printf("%c", c);
                }
        }
        printf("\n");

        return EXIT_SUCCESS;
}