cppreference.com > C++ Strings > append
append
Syntax:
  #include <string>
  string& append( const string& str );
  string& append( const char* str );
  string& append( const string& str, size_type index, size_type len );
  string& append( const char* str, size_type num );
  string& append( size_type num, char ch );
  string& append( input_iterator start, input_iterator end );

The append() function either:

For example, the following code uses append() to add 10 copies of the '!' character to a string:

   string str = "Hello World";
   str.append( 10, '!' );
   cout << str << endl;		
		

That code displays:

   Hello World!!!!!!!!!!		
		

In the next example, append() is used to concatenate a substring of one string onto another string:

 string str1 = "Eventually I stopped caring...";
 string str2 = "but that was the '80s so nobody noticed.";		

 str1.append( str2, 25, 15 );
 cout << "str1 is " << str1 << endl;		
		

When run, the above code displays:

 str1 is Eventually I stopped caring...nobody noticed.