Remove Duplicate Characters from a String

Code

#include <stdio.h>
#include <stdint.h>
#include <string.h>

void remove_duplicates(char *str) {
    char arr_val[128] = {0};
    int idx_new = 0;
    int idx_old = 0; 

    while (str[idx_old] != '\0')
    {
        if (arr_val[str[idx_old]] == 0)
        {
            arr_val[str[idx_old]]++; 
            str[idx_new] = str[idx_old];
            idx_new++; 
        }

        idx_old++;
    }

    str[idx_new] = '\0';
}

int main() {
    char str[101];
    fgets(str, sizeof(str), stdin);

    // Remove newline
    uint8_t i = 0;
    while (str[i]) {
        if (str[i] == '\n') {
            str[i] = '\0';
            break;
        }
        i++;
    }

    remove_duplicates(str);
    printf("%s", str);
    return 0;
}

Solving Approach