136 lines
3.2 KiB
C
136 lines
3.2 KiB
C
#include <cs50.h>
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#include <stdio.h>
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#include <math.h>
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void invalid(void);
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void card_check(long user_input, int nDigits);
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int start_digits(long);
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bool luhn_algo(long user_input, int nDigits);
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int main(void)
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{
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//takes user input and check if the value is positive number
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long user_input = get_long("Enter credit card number:");
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if (user_input < 1)
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{
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invalid();
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}
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//calculates the lenght of input and if correct, continues with card_check
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int nDigits = floor(log10(user_input)) + 1;
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if (nDigits == 15 || nDigits == 13 || nDigits == 16)
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{
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card_check(user_input, nDigits);
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}
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else
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{
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invalid();
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}
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}
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//gives invalid output message to user
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void invalid(void)
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{
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printf("INVALID\n");
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}
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int start_digits(long user_input)
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{
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while (user_input >= 100)
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{
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user_input /= 10;
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}
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return user_input;
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}
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//luhn algoritm to check validity of card number
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bool luhn_algo(long user_input, int nDigits)
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{
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//creates array and sets first value to last digit of user input number
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int n[nDigits];
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n[0] = user_input % 10;
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//loops through the remaining digits and stores them in the array as well (from back to the beginning)
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int i = 1;
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while (user_input >= 1)
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{
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user_input /= 10;
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n[i] = user_input % 10;
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i++;
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}
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//creates another array and fills it with every other digit multiplied by 2, starting at 2nd to last position
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int check_sum = 0;
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int check_digits[nDigits / 2];
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int j = 0;
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for (i = 1; i < nDigits; i += 2)
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{
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check_digits[j] = n[i] * 2;
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j++;
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}
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//creates sum of digits from array created above
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for (i = 0; i < nDigits / 2; i++)
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{
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//neccessary check for values with more than 1 digit, to create sum of their digits
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if (check_digits[i] > 9)
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{
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check_sum = check_sum + check_digits[i] % 10;
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while (check_digits[i] > 9)
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{
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check_digits[i] /= 10;
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}
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check_sum = check_sum + check_digits[i];
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}
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else
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{
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check_sum = check_digits[i] + check_sum;
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}
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}
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//adds sum of all digits that were not multiplied by 2 previously
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for (i = 0; i < nDigits; i += 2)
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{
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check_sum = n[i] + check_sum;
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}
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//checks if the last number of final check_sum is 0 and returns true or false
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if (check_sum % 10 == 0)
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{
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return true;
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}
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else
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{
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invalid();
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return false;
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}
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}
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//checks for the beginning numbers and branches into correct card provider
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void card_check(long user_input, int nDigits)
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{
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int beginning = start_digits(user_input);
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if (beginning == 34 || beginning == 37)
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{
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//check validity of card by using luhn alghoritm
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if (luhn_algo(user_input, nDigits))
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{
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printf("AMEX\n");
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}
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}
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else if (beginning > 39 && beginning < 50)
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{
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if (luhn_algo(user_input, nDigits))
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{
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printf("VISA\n");
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}
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}
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else if (beginning > 50 && beginning < 56)
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{
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if (luhn_algo(user_input, nDigits))
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{
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printf("MASTERCARD\n");
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}
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}
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else
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{
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invalid();
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}
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}
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