控制可能會到達非空函數的末尾。 C

Question

我在此代碼的返回行上收到上述錯誤。

// Finds the length of the card number 
int find_length(long long n)
{
    int len;
    for (len = 0; n != 0; n /= 10, len++)
    return len;
}

完整代碼：

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



void print_credit_card_brand(long long ccn);
bool check_validity(long long credit_card_number);
int find_length(long long n);
bool checksum(long long ccn);



int main(void)
{
    long long credit_card_number;
    do
    {
        credit_card_number = get_long_long("Enter valid credit card number without spaces or hyphens: ");
    } while (credit_card_number < 0);

    if (check_validity(credit_card_number) == true)
        print_credit_card_brand(credit_card_number);
    else
        printf("INVALID\n");
}



// Checks validity of credit card
bool check_validity(long long credit_card_number)
{
    int len = find_length(credit_card_number);
    return (len == 13 || len == 15 || len == 16) && checksum(credit_card_number);
}



// Finds the length of the card number 
int find_length(long long n)
{
    int len;
    for (len = 0; n != 0; n /= 10, len++)
    return len;
}



// Determines validity using Luhn’s Algorithm
bool checksum(long long ccn)
{
    int sum = 0;
    for (int i =0; ccn != 0; i++, ccn /=  10)
    {
        if (i % 2 == 0)
             sum += ccn % 10;
        else
        {
            int digit = 2 * (ccn % 10);
            sum += digit / 10 + digit % 10;
        }
    }
    return (sum % 10) == 0;
}



// Prints results besed on length of credit card and 1st 2 digits
void print_credit_card_brand(long long ccn)
{
    if ( (ccn >= 34e13 && ccn < 35e13) || (ccn >= 37e13 && ccn < 38e13) )
        printf("AMEX\n");
    else if (ccn >= 51e14 && ccn < 56e14)
        printf("MASTERCARD\n");
    else if ( (ccn >= 4e12 && ccn < 5e12) || (ccn >= 4e15 && ccn < 5e15) )
        printf("VISA\n");
    else
        printf("INVALID\n");
}

Answer 1

您忘記在 for 循環后放置分號。 所以這個錯字的功能看起來像

int find_length(long long n)
{
    int len;
    for (len = 0; n != 0; n /= 10, len++)
    {
        return len;
    }
}

該函數可以通過以下方式查找示例

unsigned int find_length( unsigned long long n )
{
    const unsigned long long Base = 10;
    unsigned int len = 0;

    for ( ; n != 0; n /= Base )
    {
        ++len;
    }

    return len;
}

注意你應該使用無符號整數類型。 否則用戶可以輸入一個負數，你的程序將產生錯誤的結果。