MY LOGIC TO SOLVE THIS PROBLEM.

string a, b; cin >> a; cin >> b;

cout << a.length() << " " << b.length() << endl;  
cout << (a + b) << endl;

char first_char_a = a[0];
char first_char_b = b[0];
a[0] = first_char_b;
b[0] = first_char_a;

cout << a << " " << b << endl;