Luhn算法的for循环中的未知值 [英] Unknown value in for loop for Luhn algorithm

问题描述

我有这段代码，由于某些原因，我在for循环的每次迭代中都会得到非常多的数字，因此我无法弄清楚逻辑.

i have this code and for some reasons i get a very large number at every iteration of the for loop and i can't figure out the logic.

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

int main(void)
{
    long CARD, digits, digit, odd, sum;

// prompting the user for a positive card number and checking the length  
    do
    {
        CARD = get_long("Please insert your card number: ");
        digits = floor(log10(labs(CARD)) + 1);
    }
    while (digits < 9 || digits > 16);

// Getting every other digit from the end (starting with the second to last)and adding the digits together   
    for (int i = 0; i < digits; i++)
    {
        CARD /= 10;
            printf("%ld\n", CARD);
        odd = CARD % 10;
            printf("%ld\n", odd);
        sum = sum + odd;
            printf("%ld\n", sum);
        CARD /= 10;
    }
}

好吧，所以我输入数字1234567890并通过do-while循环，当我进入for循环时，我得到了这些值(显示的前3个):

Ok, so i enter the number 1234567890 and pass the do-while loop and when i enter the for loop i get these values (first 3 i display):

123456789

123456789

9

140443976194473(但我希望这是9)

140443976194473 (but i expect this to be 9)

推荐答案

您尚未初始化 sum..应将其定义为 long sum = 0; 或设置为 0 ，然后再使用它.– 风向标

You have not initialised sum. It should be defined as long sum = 0; or set to 0 before you use it. – Weather Vane

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