Lab 1 Part 2: IMEI Validation

This part of the lab is worth 5 marks.

Every handphone is assigned a unique 15-digit number known as the "International Mobile Equipment Identity" or IMEI. If you own a handphone and would like to check the IMEI, simply key in *#06#. If the number displayed is more than 15 digits, simply take the first 15 digits. This 15-digit sequence comprises of the following:

• The first eight digits comprises the type approval code (TAC)
• The next six digits comprises the serial number (SNR)
• The last digit is the check digit (CD)

Objective

Write a C program imei.c that repeatedly accepts the following input:

• a eight-digit TAC;
• a six-digit SNR; and
• a one-digit CD

We shall assume that the user obeys instructions and you do not have to explicitly check the validity of the input. For each set of three numbers entered, the TAC and SNR will be used to compute the correct check digit, which will then be compared with CD to determine the validity of the IMEI. The program terminates as soon as a negative number is entered for any of the three input.

The algorithm for determining the check digit is given in the next section. The skeleton code and sample output are also provided. Remember to submit your program before the stipulated deadline for your lab session. The file that you submit must be named imei.c, any other name is not allowed.

Note that you are NOT to use any form of arrays in your program.
However, you may define functions to assist in making your code more modular.

Algorithm

Consider the example:

1. Double the values of the even labelled digits d₂, d₄, ... d₁₄. Odd labelled digits remain the same.
   For the above example,

   TAC								SNR
   d1	d2	d3	d4	d5	d6	d7	d8	d9	d10	d11	d12	d13	d14
   1	4	3	8	5	12	7	16	1	4	3	8	5	12

   
   
2. Add together the individual single digits of all the numbers obtained in step 1.
   For the above example,

   1 + 4 + 3 + 8 + 5 + (1 + 2) + 7 + (1 + 6) + 1 + 4 + 3 + 8 + 5 + (1 + 2) = 62

3. If the number obtained in step 2 ends in 0, then set the check digit to be 0. If the number obtained in step 2 does not end in 0, then set the check digit to be that number subtracted from the next higher number which does end in 0. (You might want to re-formulate this step in another way)
   For the above example, since 62 does not end with a 0, take

   70 - 62 = 8

   so the correct check digit should be 8.

Program Skeleton

#include <stdio.h>

/* Function to read input from the user. Do not modify */
int readInput(char *prompt)
{
   int value;

   printf("%s (-ve to exit): ", prompt);
   scanf("%d", &value);
   return value;
}

/** Include other functions if you feel it is necessary...
    Marks will NOT be deducted even if you do not define functions **/


/* Main function */
int main()
{
   int TAC, SNR, CD;
   /** Declare other variables here */

   while ( ( (TAC = readInput("Enter the 8-digit TAC")) >= 0) &&
           ( (SNR = readInput("Enter the 6-digit SNR")) >= 0) &&
           ( (CD = readInput("Enter the 1-digit CD ")) >= 0) )
   {
      /** You need only modify the loop body to achieve your task **/
      printf("The IMEI entered is %d-%d-%d\n\n", TAC, SNR, CD);
   }

   /* Terminating Program */
   printf("\nProgram Terminated...\n");
   return 0;
}

Sample Output

The following is a sample session. User input is denoted in bold.

Enter the 8-digit TAC (-ve to exit): 12345678
Enter the 6-digit SNR (-ve to exit): 123456
Enter the 1-digit CD  (-ve to exit): 8
This is a valid IMEI.

Enter the 8-digit TAC (-ve to exit): 12345678
Enter the 6-digit SNR (-ve to exit): 123456
Enter the 1-digit CD  (-ve to exit): 0

This is an INVALID IMEI!

Enter the 8-digit TAC (-ve to exit): 35007752
Enter the 6-digit SNR (-ve to exit): 323751
Enter the 1-digit CD  (-ve to exit): 3

This is a valid IMEI.

Enter the 8-digit TAC (-ve to exit): 20450035
Enter the 6-digit SNR (-ve to exit): 385709
Enter the 1-digit CD  (-ve to exit): 0

This is a valid IMEI.

Enter the 8-digit TAC (-ve to exit): 12345678
Enter the 6-digit SNR (-ve to exit): -1

Program Terminated...