我有这个 Luhn 算法的 C 代码。通过测试一些信用卡号码运行没问题，但是代码检查给了我这些错误。为什么？

Question

我有 Luhn 算法的 C 代码。通过测试一些信用卡号码运行没问题，但是代码检查给了我这些错误。为什么？

当运行代码时，所有信用卡号码都被正确检查，但代码检查是这样说的：应为“xxxx”，而不是“”，如下所示。

文件名为credittest.c

代码如下

the error check gives these errors below:

~/pset1/credit/ $ check50 cs50/problems/2020/x/credit
Connecting.....
Authenticating....
Verifying.....
Preparing.....
Uploading............
Waiting for results...........................
Results for cs50/problems/2020/x/credit generated by check50 v3.1.2
:) credit.c exists
:) credit.c compiles
:( identifies 378282246310005 as AMEX
    expected "AMEX\n", not ""
:( identifies 371449635398431 as AMEX
    expected "AMEX\n", not ""
:( identifies 5555555555554444 as MASTERCARD
    expected "MASTERCARD\n", not ""
:( identifies 5105105105105100 as MASTERCARD
    expected "MASTERCARD\n", not ""
:( identifies 4111111111111111 as VISA
    expected "VISA\n", not ""
:( identifies 4012888888881881 as VISA
    expected "VISA\n", not ""
:( identifies 1234567890 as INVALID
    expected "INVALID\n", not ""
:( identifies 369421438430814 as INVALID
    expected "INVALID\n", not ""
:( identifies 4062901840 as INVALID
    expected "INVALID\n", not ""
:( identifies 5673598276138003 as INVALID
    expected "INVALID\n", not ""
:( identifies 4111111111111113 as INVALID
    expected "INVALID\n", not ""

下面是代码：


//prompts the user for a credit card number and then reports (via printf) whether
//it is a validity American Express, MASTERCARD, or Visa card number

//All American Express numbers 15-digit start with 34 or 37;
//most MASTERCARD numbers 16-digit start with 51, 52, 53, 54, or 55
///all Visa numbers 13- and 16-digit start with 4


#include<stdio.h>
#include<cs50.h>
#include<math.h>
bool validity(long cardnumber);
int find_length(long cardnumber);
bool checksum(long cardnumber);
void printcardbrand(long cardnumber);



int main(void)
{
    long cardnumber;

    do
    {
        cardnumber = get_long("What is the card number: ");
    }
    while (cardnumber < 0);



    if (validity(cardnumber))
    {
        printcardbrand(cardnumber);
    }

    else
    {
        printf("INVALID\n\n");
    }

}



bool validity(long cardnumber)
{
    int len = find_length(cardnumber);

    if((len == 13 || len == 16) && checksum(cardnumber) && ((cardnumber >= 4e12 && cardnumber < 5e12)|| (cardnumber >= 4e15 && cardnumber < 5e15)))
    return true;

    if(len == 16 && checksum(cardnumber) && (cardnumber >= 51e14 && cardnumber < 56e14))
    return true;

    if(len == 15 && checksum(cardnumber) && ( (cardnumber >= 34e13 && cardnumber < 35e13) || (cardnumber >= 37e13 && cardnumber < 38e13) ) )
    return true;

    else
    return false;

}




int find_length(long cardnumber)
{
    int len;

    for (len = 0; cardnumber != 0; cardnumber /= 10)
    {
        len++;
    }
    return len;
}



bool checksum(long cardnumber)
{
    int sum = 0;

    for (int i = 0; cardnumber != 0; i++, cardnumber /=10)
    {
        if (i % 2 == 0)
        {
            sum = sum + cardnumber % 10;  //get remainder, i.e. the even index digit
        }

        else
        {
            int digit = 2 * (cardnumber % 10);
            sum = sum + digit / 10 + digit % 10;
        }
    }

    return (sum % 10) == 0;

}





void printcardbrand(long cardnumber)
{
    if ( (cardnumber >= 34e13 && cardnumber < 35e13) || (cardnumber >= 37e13 && cardnumber < 38e13) )
    {
        printf("AMEX\n\n");
    }

    else if ( (cardnumber >= 51e14 && cardnumber < 56e14) )
    {
        printf("MASTERCARD\n\n");
    }

    else if ( (cardnumber >= 4e12 && cardnumber < 5e12) || (cardnumber >= 4e15 && cardnumber < 5e15) )
    {
        printf("VISA\n\n");
    }


}



// checksum, card length, starting digits will decide which card it is.

//last line of output be AMEX\n or MASTERCARD\n or VISA\n or INVALID\n


``

Answer 1

你的 printf 调用说 "AMEX\n\n" 而它应该是 "AMEX\n"

check50 的措辞不是很好，从技术上讲，您按字面意思做了，但这不是他们的意思。 Check50 说期待 "AMEX\n" 但终端中的输出应该是 AMEX 全部单独在一行上。为此，您需要使用以下代码。

printf("AMEX\n")

显然所有其他信用卡都一样

我有这个 Luhn 算法的 C 代码。通过测试一些信用卡号码运行没问题，但是代码检查给了我这些错误。为什么？

I have this C code for Luhn’s Algorithm. it is running fine by testing some credit card numbers, but the code checking gives me these errors. Why?

c

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luhn

我有这个 Luhn 算法的 C 代码。通过测试一些信用卡号码 运行 没问题，但是代码检查给了我这些错误。为什么？

I have this C code for Luhn’s Algorithm. it is running fine by testing some credit card numbers, but the code checking gives me these errors. Why?

c

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我有这个 Luhn 算法的 C 代码。通过测试一些信用卡号码运行没问题，但是代码检查给了我这些错误。为什么？