// Dick.	cs201/lab/04
// Date Sun Apr 23 11:31:41 PDT 1995
// Teaching how functions work

/* 
This program shows you how a functions with reference arguments work.
To do this it has special tracing commands that report
what it is doing to the special diagnostic output channel "cerr".

It also shows that you don't have to store a value before printing it.

The calculation is not very exciting.... 

This is not a very good style because
	there is no need
	to use call by reference when only _________________result is
	returned.
*/

#include <iostream.h>

int main( ) 
{ 
  // Main's local variable is
	int n;
  //Use the following functions
	void odd(int&);
	void half(int&);
	void dubl(int&);//Experiment a:  Delete the & here and in the
			// function definition of dubl below
			//  and make it compile and run.  Does it do
			//  the same things?
			// If it does put the & back in
	void trbl(int&);
	void next(int&);

  // Start of commands in main

	n=0;
			//Experiment b: is this valid here
			//		next(0);

	cout <<"In main,  n is now "<<n<<endl;
	next(n);
	cout <<"In main,  n is now "<<n<<endl;
	dubl(n);
	cout <<"In main,  n is now "<<n<<endl;
	half(n);
	cout <<"In main,  n is now "<<n<<endl;
	odd(n);
	cout <<"In main,  n is now "<<n<<endl;
	trbl(n);
	cout <<"In main,  n is now "<<n<<endl;

	return 0;
}


//-------------------------------------------------------------------


void odd(int& m) //Puts 1 into m, if m is odd and zero otherwise
{
	cerr<<"\n\tEntering 'odd' with argument m equal to "<<m<<endl;
	m = m%2;
	cerr<<"\n\tLeaving 'odd' with argument m equal to "<<m<<endl;
}

//-------------------------------------------------------------------


void half(int& m)//Divides m by 2 (rounded down)
{
	cerr<<"\n\tEntering 'half' with argument m equal to "<<m<<endl;
	m = m/2;
	cerr<<"\n\tLeaving 'half' with argument m equal to "<<m<<endl;
}

//-------------------------------------------------------------------


void dubl(int& m)//Experiment a:  Delete the & here and the prototype
		// for dubl() above
{
	cerr<<"\n\tEntering 'dubl' with argument m equal to "<<m<<endl;
	m = m+m;
	cerr<<"\n\tLeaving 'dubl' with argument m equal to "<<m<<endl;
		//Experiment c: What happens if you add the following
		// return m*m;
			// the star above is not a typo!
		/// Remove it when you have found out.
}

//-------------------------------------------------------------------


void trbl(int& n)
{
	cerr<<"\n\tEntering 'trbl' with argument n equal to "<<n<<endl;
	n = n + n + n;
	cerr<<"\n\tLeaving 'trbl' with argument n equal to "<<n<<endl;
}

//-------------------------------------------------------------------


void next(int& n)
{
	cerr<<"\n\tEntering 'next' with argument n equal to "<<n<<endl;
	n = n+1;
	cerr<<"\n\tLeaving 'next' with argument n equal to "<<n<<endl;
}

//Exercise d: in the above functions, are n and m IN, OUT or INOUT
//	arguments?