Convert HEX string without spaces into an array of bytes

hex_str_to_byte.c

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

int main(void)
{
    char s[] = "CAFEDEADBEEF010203040506";
    size_t len = strlen(s);
    unsigned char bytes[len / 2];

    for (size_t i = 0; i < len; i += 2)
    {
        if (!isxdigit(s[i]) || !isxdigit(s[i + 1]))
        {
            puts("Convert error");
            break;
        }

        sscanf(s + i, "%2hhx", &bytes[i / 2]);
    }

    for (size_t i = 0; i < sizeof bytes; ++i)
    {
        printf("%02X", bytes[i]);
    }
    puts("");

    return 0;
}