add to binary strings (solved)

#pragma GCC optimize ("O3")
#pragma GCC target ("sse4")

#include <bits/stdc++.h>
using namespace std;

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<string,int> psi;
typedef vector<int> vi;
typedef vector<string> vs;
typedef vector<ll> vll;
typedef vector<vector<int>> vvi;
typedef vector<vector<string>> vvs;
typedef vector<vector<ll>> vvll;

#define FOR(i, a, b) for (auto i=a; i<=(b); i++)
#define FORd(i,b,a) for (int i =b; i >= a; i--)
#define sz(x) (int)(x).size()
#define mp make_pair
#define pb push_back
#define f first
#define s second
#define ins insert

const int MOD = 1000000007;
//type functions here

int m(ll k)
{
    return k%MOD;
}
string resize(string x,int count)
{
    while(count--)
    {
        x="0"+x;
    }
    return x;
}
int main() {

    int tc=1;
    //cin>>tc;
    FOR(i,1,tc){
     string a="1",b="11";
     int m=a.length()-1,n=b.length()-1;
     if(m<n) {a=resize(a,n-m);m=n;}
     if(n<m) {b=resize(b,m-n);n=m;}
     int carry=0;
     string ans="";
     while(m!=-1||n!=-1)
     {
        if(a[m]=='0'&&b[n]=='0')
       {
           ans=to_string(0+carry)+ans;
           carry=0;
       }
       else if(a[m]=='1'&&b[n]=='1')
       {
           ans=to_string(0+carry)+ans;
           carry=1;
       }
       else
       {
           if(carry)
           {
               ans=to_string(0)+ans;
           }
           else
           {
               ans=to_string(1)+ans;
           }
       }

        cout<<ans<<endl;

        m--;
        n--;
     }
     if(carry) ans=to_string(carry)+ans ;
     cout<<ans<<endl;
    }
    return 0;
}