#include <stdio.h>

#define LEN     18

void main(){

        char id[LEN] = {0};

        int weight[] = {7,9,10,5,8,4,2,1,6,3,7,9,10,5,8,4,2};

        int validate[] = {1,0,'x'-'0',9,8,7,6,5,4,3,2,1}; 

        int i=0;

        int sum = 0;

        printf("Input your id\n");      

        for(i=0; i<LEN; i++){

                id[i] = getchar()-'0';  

                sum += id[i]*weight[i];

        }

        sum %= 11;

        printf("Your id is %s [%c]\n", validate[sum] == id[LEN-1]?"valide":"invalide", validate[sum]+'0');

}

~