First C program

first.c

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

int aiv_strlen(char *str)
{
    // 100 100
    char *original_ptr = str;

    while(*str) {
        str++;
    }

    return str - original_ptr - 1;

    /*int counter = 0;
    while(*str){
        str++;
        counter++;
    }
    return counter;*/

    /*
    while(*str++);
    return str - original_ptr - 2;
    */
}

int main(int argc, char *argv[])
{
    char player_name[99];

    if (!fgets(player_name, 99, stdin)) {
        fprintf(stderr, "mortacci tua\n");
        return -1;
    }

    int len = aiv_strlen(player_name);
    char *reversed = malloc(len + 1);
    for(int i=0;i<=len;i++) {
        reversed[len-i] = player_name[i];
    }

    fprintf(stdout, "Hello: %d %s\n", len, reversed);
    return 0;
}