String in cpp

Question

string s ;
cin >> s;
transform(s.begin(), s.end(), s.begin(), ::tolower);
cout << s;

input : Hello World
output:hello

why it only convert hello to lowercase?

Answer 1

cin only reads the first word. To read the entire line, use:
getline(cin, s);

http://www.cplusplus.com/reference/string/string/getline/

Edit: The second one.

Answer 2

char s[25];
cin.getline(s,25);

OR

string s = " ";
cin.ignore();
getline(cin, s);