C语言验证信用卡卡号是否有效

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

int luhn(const char* cc)
{
    const int m[] = {0,2,4,6,8,1,3,5,7,9}; // mapping for rule 3
    int i, odd = 1, sum = 0;

    for (i = strlen(cc); i--; odd = !odd) {
        int digit = cc[i] - '0';
        sum += odd ? digit : m[digit];
    }

    return sum % 10 == 0;
}

int main()
{
    const char* cc[] = {
        "49927398716",
        "49927398717",
        "1234567812345678",
        "1234567812345670",
        0
    };
    int i;

    for (i = 0; cc[i]; i++)
        printf("%16s\t%s\n", cc[i], luhn(cc[i]) ? "ok" : "not ok");

    return 0;
}

                                输出结果

     49927398716        ok
     49927398717        not ok
1234567812345678        not ok
1234567812345670        ok

标签：信用卡,Luhn,C语言