You can concatenate std::strings using the overloaded + and += operators. Using the + operator:
std::string hello = "Hello";
std::string world = "world";
std::string helloworld = hello + world; // "Helloworld"
Using the += operator:
std::string hello = "Hello";
std::string world = "world";
hello += world; // "Helloworld"
You can also append C strings, including string literals:
std::string hello = "Hello";
std::string world = "world";
const char *comma = ", ";
std::string newhelloworld = hello + comma + world + "!"; // "Hello, world!"
You can also use push_back() to push back individual chars:
std::string s = "a, b, ";
s.push_back('c'); // "a, b, c"
There is also append(), which is pretty much like +=:
std::string app = "test and ";
app.append("test"); // "test and test"