Programming Assignment #1 Solution

The Drunk Beetle and the Boiling Oil

 

This assignment requires that you design and implement a small C program.  It’s primary  purpose is simply to reacquaint you with C programming on a Linux system.

 

A single intoxicated beetle  is placed  in the  exact  center  of a cardboard square  that is suspended over a large vat  of boiling oil.  The beetle,  being quite  drunk,  behaves  rather erratically. It moves exactly  1 inch (in 1 second) in a straight line in a randomly  chosen direction.   It  then  passes out for exactly  1 second.  When  it wakes, it again picks a random  direction  and moves 1 inch.  We are interested in selling insurance  to drunk  beetles  on squares  suspended  above vats  of boiling oil, so we want to compute  the  average  time  that a drunk  beetle  will live after  it starts to move for the first time.   Clearly,  the  way to get a handle  on this  average  is to measure  the  time  it takes  for a beetle  to get boiled for lots of beetles,  and  then  compute  the  average  over the  sample.   To make the problem a bit easier, assume that the last movement by the beetle lasts a full second.  That is, don’t worry about  taking  into account the fact that the last movement of the beetle will neither  be a full inch nor a full second.

 

You should check out the manual  pages for:

 

• random(), the “better” random  number  generator on our system,

 

• sin(), cos(), etc., the trigonometric functions,

 

• printf(), the  formatted output facility  (especially  the  material  about  formatted output of floating point numbers), and

 

• atoi(), and related  functions  that convert  strings  into numeric  quantities.

 

Note that the  trig  functions  are part  of the  mathematics library  on our systems.  This means you have to tell the  linker to include that library  explicitly.   If your source program  is called beetle.c, and you want an executable  called beetle, do the following:

 

gcc -Wall -o beetle beetle.c -lm

 

A final  requirement:  your  program  should  be  parametric in  that two command  line  argument control  your simulation:

 

• The first argument is a positive  nonzero integer  which specifies the length  of one side of the square in inches.  This integer must  not underflow nor overflow the machine representation of a long integer  (you must  enforce this).

 

• The second argument is a positive nonzero integer which specifies how many beetles are boiled in order to get the average lifetime.  This integer must not underflow nor overflow the machine representation of a long integer  (again,  you must  enforce this).

For example,  if your binary  is called beetle, the command  line

 

./beetle 20 10000

 

will simulate  the actions  of 10000 beetles on a 20” by 20” square in order to compute  mean beetle lifetime.

 

Make  sure  that your  program  exits  gracefully  with  an  error  message  for “bad”  command  line arguments. Argument checking is a significant component of this assignment (and  the course).

 

 

Submission

 

I  will post  the  details  of project  submission  shortly,   but  you  will be  required  to  submit  your source, which the  TA will compile and execute  on a Linux system  in the  departmental lab in 121

McGlothlin-Street Hall.  Bear this in mind if you do your development on another  platform. Your output for a run should appear  exactly  like the following line:

X by X square, Y beetles, mean beetle lifetime is Z.Z

 

where X and  Y are integers  and  Z.Z is a real (show only a single digit  to the  right of the  decimal point).  A concrete  example:

 

% ./beetle 10 10000

10 by 10 square, 10000 beetles, mean beetle lifetime is 67.0

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