// abcd.C -- This is a modular C++ program that features
// functions calling other functions (i.e. nested function calls).

#include <iostream.h>

void a();
void b();
void c();
void d();

int main()
{
  a();
  cout << endl;
  b();
  cout << endl;
  c();
  cout << endl;
  d();
  cout << endl;

  return 0;
}

void a()
{
  cout << "a";
}

void b()
{
  a();
  cout << "b";
}

void c()
{
  a();
  b();
  cout << "c";
}

void d()
{
  a();
  b();
  c();
  cout << "d";
}

//////////////////////////////////
// The output of the program is:
// a
// ab
// aabc
// aabaabcd
//////////////////////////////////