Multiply by 11

#include<iostream>
#include<string>
using namespace std;

int multiply(int a[], int n){
    int i;
    unsigned long long int cary = 0;
    for(i = 0; i < n; i++){
        int k = a[i] * 11 + cary;
        a[i] = k % 10;
        cary = k / 10;
    }
    int index = n;
    while(cary){
        a[index++] = cary % 10;
        cary /= 10;
    }
    return index;
}

int main(){
    int t; cin >> t;
    while(t--){
        string input;
        //  Taking input
        cin >> input;
        unsigned int n = input.length();
        int a[n*10] = {0}, i, j;

        //  converting string into integer
        for(i = n-1, j = 0; i > -1; i--, j++){
            a[i] = input[j] - '0';
        }
        //  Showing the int array
        //for(i = 0; i < n; i++) cout << a[i];
        int index = multiply(a, n);

        //  Showing result
        for(i = index-1; i > -1; i--){
            cout << a[i];
        }
        cout << endl;
    }
}