specifically about strings on C

Question

I am just a beginning in C and my question is on the topic of strings. I'm studying from a blog who gives the content and then a few questions, one of which is to code a program that reads a string (being specific, a word) and returns which of the letters of the word is repeated. I did the code but when I run it, it returns @@. Can someone help me or tell me where is the mistake? code below:

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

int main()
{
    char word[11];
    int running1;
    int running2;
    char repeated[11];

    printf("Give us a word:");
    fgets(word, 11, stdin);
    printf("word:%s", word);

    for (running1 = 0; running1 < 10; running1++)
        for (running2 = 0; running2 < 10; running2++)
            if(word[running1] == word[running2])
            {
                word[running1] = repeated;
            }

    printf("\nletters repeated:%s", repeated);
}