#include <iostream.h>

// file: mondias.cc
// using user-defined functions
// functions calling functions

int main()
{
   Diamond2();

   return 0;
}

void Diamond2()
{
   Diamond();
   Diamond();
}

void Diamond()
{
	Dia();
	Mond();
}

void Mond()
{
	cout << " ***** " << endl;
	cout << "  ***  " << endl;
	cout << "   *   " << endl;
}

void Dia()
{
	cout << "   *   " << endl;
	cout << "  ***  " << endl;
	cout << " ***** " << endl;
	cout << "*******" << endl;
}

Will not compile:

<make mondias
>g++ -I/usr/project/courses/cps008/lib -g mondias.cc -o mondias -lm /usr/project/courses/cps008/lib/libtapestry.a -lg++
>mondias.cc: In function `int main()':
>mondias.cc:9: warning: implicit declaration of function `int Diamond2(...)'
>mondias.cc: In function `void Diamond2()':
>mondias.cc:16: warning: implicit declaration of function `int Diamond(...)'
>mondias.cc: In function `void Diamond()':
>mondias.cc:22: warning: implicit declaration of function `int Dia(...)'
>mondias.cc:23: warning: implicit declaration of function `int Mond(...)'
>Undefined                       first referenced
> symbol                             in file
>Dia                                 /tmp/cca003NS1.o
>Diamond                             /tmp/cca003NS1.o
>Mond                                /tmp/cca003NS1.o
>Diamond2                            /tmp/cca003NS1.o
>ld: fatal: Symbol referencing errors. No output written to mondias
>*** Error code 1
>make: Fatal error: Command failed for target `mondias'