Using strings in C++ as a data type

Problem link for strings

Code : 
#include<iostream>
#include<string>
using namespace std;
int main(){
    string a, b;
    cin>>a>>b;
    int len_a, len_b;
    len_a = a.size();
    len_b = b.size();
    cout<<len_a<<" "<<len_b<<endl;
    string c;
    c = a+b;
    cout<<c<<endl;
    char temp;
    // now swapping first character of the strings
    temp = a[0];
    a[0] = b[0];
    b[0] = temp;
    cout<<a<<" "<<b<<endl;
    return 0;
}