#includeIn this example, we create an empty string and reserve memory for 100 characters. Then we add two strings to the original string using the += operator. Finally, we print the resulting string which will contain "hello world". This example uses the C++ STL (Standard Template Library). Library: C++ STL (Standard Template Library)#include int main() { std::string str; str.reserve(100); // preallocate memory for 100 characters str += "hello"; str += " world"; std::cout << str << std::endl; return 0; }