Remove Duplicate Characters from a String

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

void remove_duplicates(char *str) {
	if (str==NULL) return;
    int res[256]={0};
    int j = 0;
    for (int i = 0; str[i] != '\0'; i++) {
        unsigned char val = (unsigned char) str[i];
        if (res[val]==0){
            res[val]=1;
            str[j] = str[i];
            j++;
        }
    }
    str[j] = '\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;
}