Help,why taking XOR of each corresponding bit and appending it to final string d

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# include

# define ll long long int

# define MOD 1000000007

# define pii pair

# define pb push_back

# define pp pop_back

# define vi vector

using namespace std; void solve(){ int n; cin>>n; vectora; for(int i=0;i>x; a.pb(x); } if(n==1){ if(a[0] == "1"){ cout<<0<>t; while(t--){ solve(); } return 0; }```