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credit.c

JiriKiner Aug 23rd, 2019 169 Never
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  1. // This program will check if the credit or debit card is valid using the Luhn's algorithm. It can check the American Express, Master Card and VISA cards
  2.  
  3. #include <stdio.h>
  4. #include <cs50.h>
  5.  
  6. // Functions needed to calculate part of the Luhn's algorithm
  7. int odd(long number);
  8. int even(long number);
  9.  
  10. int main(void)
  11. {
  12.     // Declaration of variable "number" (for input from user) and card to check the card type
  13.     long number = 0;
  14.     int card = 0;
  15.     // Loop to get valid input from the user
  16.     do
  17.     {
  18.         // Data type "long" so there will be enough memory for a valid card number
  19.         number = get_long("Number: ");
  20.         // Checking the card type and storing it to variable "card", if wrong type, invalid number or string, prompting the number again
  21.         // 0 = INVALID
  22.         // 1 and 2 = AMEX (15 digits)
  23.         // 3 = MASTERCARD (16 digits)
  24.         // 4 and 5 = VISA (13 and 16 digits)
  25.         if (number > 339999999999999.9 && number < 349999999999999.9)
  26.         {
  27.             // AMEX 1
  28.             card = 1;
  29.         }
  30.         else if (number > 369999999999999.9 && number < 379999999999999.9)
  31.         {
  32.             // AMEX 2
  33.             card = 2;
  34.         }
  35.         else if (number > 5099999999999999.9 && number < 5599999999999999.9)
  36.         {
  37.             // MASTERCARD
  38.             card = 3;
  39.         }
  40.         else if (number > 3999999999999.9 && number < 4999999999999.9)
  41.         {
  42.             // VISA 1
  43.             card = 4;
  44.         }
  45.         else if (number > 3999999999999999.9 && number < 4999999999999999.9)
  46.         {
  47.             // VISA 2
  48.             card = 5;
  49.         }
  50.         else
  51.         {
  52.             // INVALID
  53.             printf("INVALID\n");
  54.             exit(0);
  55.         }
  56.     }
  57.     while (card != 1 && card != 2 && card != 3 && card != 4 && card != 5);
  58.     // Checking validity of the card
  59.     int a = even(number);
  60.     int b = odd(number);
  61.     int check = ((a + b) % 10);
  62.     if (check == 0)
  63.     {
  64.         if (card == 1 || card == 2)
  65.         {
  66.             printf("AMEX\n");
  67.         }
  68.         else if (card == 3)
  69.         {
  70.             printf("MASTERCARD\n");
  71.         }
  72.         else if (card == 4 || card == 5)
  73.         {
  74.             printf("VISA\n");
  75.         }
  76.     }
  77.     else
  78.     {
  79.         printf("INVALID\n");
  80.     }
  81. }
  82.  
  83. // Function for calculating the odd numbers total
  84. int odd(long number)
  85. {
  86.     int n1 = 0;
  87.     int n2 = 0;
  88.     for (long i = 0, j = 1000, k = 100; i < 7; i++)
  89.     {
  90.         n1 = ((number % j) / k);
  91.         n2 = n2 + n1;
  92.         j = j * 100;
  93.         k = k * 100;
  94.     }
  95.     int n0 = (number % 10);
  96.     int odd = n2 + n0;
  97.     return odd;
  98. }
  99.  
  100. // Function for calculating the even numbers total
  101. int even(long number)
  102. {
  103.     int n1 = 0;
  104.     int even = 0;
  105.     for (long i = 0, j = 100, k = 10; i < 8; i++)
  106.     {
  107.         n1 = (((number % j) / k) * 2);
  108.         if (n1 > 9)
  109.         {
  110.             n1 = (n1 - 9);
  111.         }
  112.         even = (even + n1);
  113.         j = j * 100;
  114.         k = k * 100;
  115.     }
  116.     return even;
  117. }
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