Write a function with this prototype:

 #include 

 void numbers(ostream& outs, const String& prefix, unsigned int levels);

The function prints output to the ostream outs. The output consists of the String prefix followed by "section numbers" of the form 1.1., 1.2., 1.3., and so on. The levels argument determines how may levels the section numbers have. For example, if levels is 2, then the section numbers have the form x.y. If levels is 3, then section numbers have the form x.y.z. The digits permitted in each level are always '1' through '9'. As an example, if prefix is the string "THERBLIG" and levels is 2, then the function would start by printing:

THERBLIG1.1.

THERBLIG1.2.

THERBLIG1.3.

and end by printing:

THERBLIG9.7.

THERBLIG9.8.

THERBLIG9.9.

The stopping case occurs when levels reaches zero (in which case the prefix is printed once by itself followed by nothing else).

The String class from has many manipulation functions, but you'll need only the ability to make a new string which consists of prefix followed by another character (such as '1') and a period ('.'). If s is the String that you want to create and c is the digit character (such as '1'), then the following statement will correctly form s:

 s = (prefix + c) + '.';

This new String s can be passed as a parameter to recursive calls of the function.