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I was doing the credit problem with the visa test card in the page: 4003600000000014

It passed that test, however in other tests it doesn't pass. I think it's a matter of the sum that it can't compute it correctly so when using modulo 10 doesn't equal 0 and prints invalid.. Also I don't know if I did the get type if statements incorrectly but I don't get how. Please help :)

Here's my code

#include <stdio.h>
#include <cs50.h>
#include <math.h>


int main(void)
{
    // Input card number
    long cardNumber;

    do
    {
        cardNumber = get_long_long("Number: ");
    }
    while(cardNumber < 0);

    // Card calculation
    int power = 0;
    int sum = 0;
    long beginNumber = (cardNumber / 10); // No modify
    long number = beginNumber;
    while (power <= 14)
    {
        // If only one number sum it
        if ( ( ( ((number%10)*2) / 10) % 10) == 0)
        {
            sum += ((number % 10) * 2);
            power += 2;
            number = beginNumber / pow(10,power);
        }
        // Sum both numbers
        else if ( ( ( ((number%10)*2) / 10) % 10) == 1)
        {
            sum += (number % 10) * 2 % 10;
            sum += (number % 10) * 2 / 10 % 10;
            power += 2;
            number = beginNumber / pow(10,power);
        }

    }
    number = cardNumber;
    power = 0;
    while (power <= 14)
    {
        sum += (number % 10);
        power += 2;
        number = number / pow(10,power);
    }

    // Is it legit?
    if (sum % 10 != 0)
    {
        printf("INVALID\n");
    }
    else if (sum % 10 == 0)
    {
        // Get type
        int visa_1 = cardNumber / pow(10, 15);
        int visa_2 = cardNumber / pow(10, 12);
        int mastercard = cardNumber / pow(10, 14);
        int amex = cardNumber / pow(10, 13);
        if ( visa_1 || visa_2 == 4 )
        {
            printf("%s\n", "VISA");
        }
        else if ( mastercard == (51 | 52 | 53 | 54 | 55) )
        {
            printf("%s\n", "MASTERCARD");
        }
        else if ( amex == (34 | 37) )
        {
            printf("%s\n", "AMEX");
        }
    }
}
1

A problem I found is at line 47 of the code (the second while loop):

while (power <= 14)
{
    sum += (number % 10);
    power += 2;
    number = number / pow(10,power);
}

I think you meant the line number = number / pow(10,power) to be:

number = beginningNumber / pow(10,power)

Otherwise the variable number does the following (during the second while loop):

iteration             "number"           "power"
 0                    378282246310005      0
 1                    3782822463100        2
 2                    378282246            4
 3                    378                  6
 4                    0                    8
 5                    0                   10
 6                    0                   12
 7                    0                   14
 8                    0                   16

Another problem is the way comparisons are written. In C the name of the variable has to be repeated every time instead of the way this code is written. And the OR operator should be a double pipe || instead of a single pipe |:

Instead of this:

if ( visa_1 || visa_2 == 4 )

Each one has to be compared like this:

if (visa_1 == 4 || visa_2 == 4)

And instead of this:

else if ( mastercard == (51 | 52 | 53 | 54 | 55) )

and this:

else if ( amex == (34 | 37) )

Double pipes must be used as an OR operator, and compare each number (or use less than < and greater than signs > to work with a range of values):

else if ( amex == 34 || amex == 37 )

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