我定义的条件循环不按预期运行是否正常？

Question

刚开始哈佛的CS50课程。我目前正在处理问题集 1，即验证信用卡号。为什么我的条件循环没有像预期的那样运行？例如，当我输入信用卡号 len 16 并且不符合给定的条件（例如：59e14）时，它仍然会打印出“MASTERCARD”？

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

// Declaration of the functions
long get_number(void);
//const char * check_len(long cc);
void check_len(long cc);

// Main program
int main(void)
{
    int i;
    long credit_number = get_number();
    printf("Validation for %ld\n", credit_number);

    check_len(credit_number);
}

// Function that prompt the user for a credit card number
long get_number(void)
{
    // Declaration of the credit card variable
    long number;

    // Ask the user for a credit card number. If it's not none-negative, keep asking
    do
    {
        number = get_long("Enter credit card number: ");
    }
    while (number <=0);
    return number;
}

// Function to check the type of credit card
void check_len(long cc)
{
    // Declaration of variables
    int i;
    long number = cc;

    // Count the len of the provided credit card number
    for (i = 0; cc != 0; i++)
    {
        cc = cc/10;
    }
    printf("%i\n", i);

    // Validate the type of card
    if (i == 15)
    {
        if ( (number >= 34e13 && number < 35e13) || (number >= 37e13 && number < 38e13) )
        printf("AMEX\n");
        else
        {
            printf("INVALID\n");
        }
    }
    else if (i == 13 || i == 16)
    {
        if ( (number >= 51e14  || number < 56e14) )
        {
            printf("MASTERCARD\n");
        }
        else if ( (number >= 4e12 || number < 5e12) || (number >= 4e15 || number <= 5e15))
        {
            printf("VISA\n");
        }
        else
        {
            printf("INVALID\n");
        }
    }
}

Answer 1

给定

 if ( (number >= 51e14  || number < 56e14) )
     ...

51e14 小于 56e14，所以每个实数要么大于 51e14 要么小于 56e14 .

如果您只想要该范围内的数字，则需要使用 && 以便满足两个条件：

 if ( ( number >= 51e14 )  && ( number < 56e14 ) )
     ...

你的其他情况看起来也有类似的问题。

我定义的条件循环不按预期运行是否正常？

Is it normal that my defined condition loop does not act like expected?

c

cs50