I know it's silly, but I just want to fix his first version with the minimum possible changes;

  /* Copyright 2023. All unauthorized distribution of this source code
     will be persecuted to the fullest extent of the law*/
  #include <stdio.h>
  #include <stdint.h>
  #include <string.h>
  int main(int argc, char* argv[])
  {
      uint8_t number = argc>1 ? argv[1][strlen(argv[1])-1]-'0' : printf("Usage: odd-or-even number\n");
      if (number == 0)
          printf("even\n");
      if (number == 1)
          printf("odd\n");
      if (number == 2)
          printf("even\n");
      if (number == 3)
          printf("odd\n");
      if (number == 4)
          printf("even\n");
      if (number == 5)
          printf("odd\n");
      if (number == 6)
          printf("even\n");
      if (number == 7)
          printf("odd\n");
      if (number == 8)
          printf("even\n");
      if (number == 9)
          printf("odd\n");
      if (number == 10)
          printf("even\n");
  }

This way it basically works. It's a shame that it doesn't call out a non numeric argument but that's about the only problem. It relies on a trick, printf() returns the number of characters printed, so the error message string needs to be longer than 10.