How to copy a string to other string ignoring cases? [duplicate]

I want to change all the characters to lowercase in a string and copy it to another string.I tried the below approach in c++ but not working as expected. It is returning the string before a whitespace.

#include<bits/stdc++.h>
using namespace std;
int main()
{
    string s,t="";
    cin>>s;
    for(int i=0;i<s.size();i++){
        t+=tolower(s[i]);
    }
    cout<<t<<"\n";
    return 0;
}

For example if i give the input string "HELLO WORLD", giving result only "hello". Ignoring anything after space.

Is there any way to solve this is C++?