检验身份证的正确性(C语言版本)

/* check id_card 
 * write by sndnvaps<sndnvaps@gmail.com>
 * ai -> a1 , a2, a3, a4, a5, a6... a17 (a18 是校验码) 身份证前17位对应(ai)
 * wi -> 7, 9, 10, 5, 8, 4, 2, 1, 6, 3, 7, 9, 10, 5, 8, 4, 2 (17位)
 *  
 *  int  res = 0;
 *  for (i = 1; i < 17; i++) {
 *          res += (a[i] * w[i])
 *          }
 *     int  y = res % 11；
 * 
 *
 * y 与 a18的对应关系
 *
 *  y    { 0, 1,  2,  3, 4, 5, 6, 7, 8, 9, 10}
 *  a18  { 1, 0, 'X', 9, 8, 7, 6, 5, 4, 3,  2 } -> vefiry[18] = { 1, 0, 'X', 9, 8, 7, 6, 5, 4, ,3, 2};
 */

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

int wi[17] = { 7, 9, 10, 5, 8 , 4, 2, 1, 6, 3, 7, 9 , 10, 5, 8, 4, 2};
int a18[11] = { 1, 0, 'X', 9, 8, 7, 6, 5, 4, 3, 2};

int char2int(char n) {
    return (n - 48);
}

int check_id(char id[17] ) {//return y
    int res = 0;
    int y;
    int i;
    for (i = 0; i < 17; i++) {
        res += (char2int(id[i]) * wi[i]);
    }
    y = res % 11;
    return y;
}


int verify_id_t(int verify_id, int id_v) { //verify_id = y; id_v = a18
    int i;
    int temp; //store the i ; 
    for (i = 0; i < 10; i++) {
        if (i == verify_id) {
            temp = a18[i];
            printf("a18[%d] = %d\n", i, temp);
            break;
        }
    }


    if (temp == id_v)
        return 1; // get it , 验证合格

    return 0;
}

void usage() {
    printf("check_id_card id_card_num \n");
}



int main(int argc, char *argv[]) {
    if (argc < 2) {
        usage();
    }

    char id_string[18];
    int id_18;
    int i;
    int y;
    if (strlen(argv[1]) > 18) {
        printf("id_card_num must be 18 bits\n");
        return 0;
    }
    strncpy(id_string, argv[1], 18);
    
    id_18 = char2int(id_string[17]);
    id_string[17] = '\0';
    printf("id_18 = %d\n", id_18);
    y = check_id(id_string);
    if(verify_id_t(y, id_18) == 1) {
        printf("verify success\n");
    } else {
        printf("verify failed\n");
    }

    return 0;
}