How to input 16 base IP adress

Hi,how can input base a 16 ip address and check it if it is correct?
Any helps and tips are appreciated.

Note:
You can't use data structures and define your own functions.
In Base 16 (Hexademical), you can only accept 0..0 and A..F
Sample output:
ENTER IP ADRESS:
AA.FF.00.00
It's correct
or
ENTER IP ADRESS
AA.256.00.00
It's wrong

I suggest clarifying the implications of "you can't use data structures and define your own functions" with your instructor: an array is a data structure and the main function would be "your own function". Having said that, my guess is that the restriction has more to do with defining structs in C and functions other than the main function.

I suggest that you start by hardcoding these test IP addresses, valid and invalid, as strings, then think of how you can validate them by analysing the content of these strings. If you can get this right, the rest is just a matter of implementing the interactive I/O to read a string.

Maybe using scanf with "%2hhX.%2hhX.%2hhX.%2hhX"? Example:

Code:

---

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

int main( void )
{
  unsigned char a[4];
  int converted;

  const static char ipstr[] = "AA.0.CC.DD";  // should pass.
  const static char ipstr2[] = "AA.256.0.10";  // should fail.

  if ( ( converted = sscanf( ipstr, "%2hhX.%2hhX.%2hhX.%2hhX", a, a+1, a+2, a+3 ) ) != 4)
  {
    if ( converted == EOF )
      perror( "sscanf" );
    else
      fprintf( stderr, "error: Only %d octects converted.\n", converted );
    return EXIT_FAILURE;
  }

  printf("%hhu.%hhu.%hhu.%hhu\n", *a, *(a+1), *(a+2), *(a+3));

  if ( ( converted = sscanf( ipstr2, "%2hhX.%2hhX.%2hhX.%2hhX", a, a+1, a+2, a+3 ) ) != 4)
  {
    if ( converted == EOF )
      perror( "sscanf" );
    else
      fprintf( stderr, "error: Only %d octects converted.\n", converted );
    return EXIT_FAILURE;
  }

  printf("%hhu.%hhu.%hhu.%hhu\n", *a, *(a+1), *(a+2), *(a+3));

  return EXIT_SUCCESS;
}

---

There is also inet_pton(), but it fails with non standard IPv4 or IPv6 addresses...

Here is the hard copy paste of the question.
Hope it makes sense now this is my first year in computer science program.We only learned about the basic math operations,if else statements and loops

BTW I asked the instructor about the strings and we can't use strings.


Update:
Please enter the Base for your IP Address (10/16):16
Please enter the IP Address:
OO.11.10.KK
This is NOT a valid IP Address!
Please enter the IP Address:
00.11.10.FF
Thanks it is a valid IP address!
Please enter the Subnet Mask:
FF.FF.FF.CO
Thanks it is a valid Subnet Mask

Please Note the following for this step:
An IP address is 32 bit value split into four 8 bit values (octet) each from 0 to 255.Therefore, you need to make the necessary checks for this format.
In Base 16 (Hexademical), you can only accept 0..0 and A..F
When the user enters invalid base (other than base 10 and base 16)
When the users enters invalid IP address or subnet mask


RULES:
You are not allowed to use data structures such as arrays to store values for theconversion operation.
You are not allowed to define your own functions.

I have updated the post with more information about the question and rules.

Sounds like your instructor wants you to validate character by character.