INF3110/4110
		   Problems week 36 (30.8-3.9.2004)

(The problem text is in English as we have foreign students who speak
littel Norwegian.)


Problem 1

Extend the i "Hello program" presented in the lecture to give your
name: 

    Hello, Xxx Xxx.

Hint: The following Perl sentence will assign your name to the $Name
variable:

	$Name = (getpwuid($<))[6];


Problem 2

Extend the problem even further to say "Good morning" or "Good
evening" depending on the time of day. More specifically, the program
should say

       "Good morning"	between 6:00 and 12:00
       "Good afternoon" between 12:00 and 18:00
       "Good evening"   between 18:00 and 22:00
       "Good night"	any other time.

Hint: The Perl sentence

     ($Sec, $Min, $Hour) = localtime(time);

will find the current time of day.


Problem 3

Extend the program even further to print the time of day, like this:

       Good evening, Xxx Xxx.
       The time is now 21:16:01.

Note that the minutes abd seconds should always be two digits, so an
extra "0" must be inserted when either of the two is less than 10.


Problem 4

We can compute the absolute value of $A by writing

   if ($A < 0) { $A = -$A; }

(The absolute value of a number is always positive. The absolute value
of 5 is 5, and the absolute value of -5 is also 5.)

Write at least 4 other Perl statements that also compute the absolute
value of a number.


Problem 5

Write e Perl program which will print the following table:

 n  n?   n?
 1   1    1
 2   4    8
 3   9   27
 4  16   64
 5  25  125
 6  36  216
 7  49  343
 8  64  512
 9  81  729
10 100 1000

Hint: The expression

      length($x)

tells how many characters there are in $x.


Problem 6

The Perl loop

    while (<>) {
       ...
    }

will loop through all lines in the files specifies as parameters; the
lines will successively be placed in $_. For example, the following
loop will count the number of lines in the files:

     while (<>) {
         ++$N_lines;
     }

Write a simplified version of the standard Unix program "wc" which
counts the number of lines and the number of bytes in the specidied
files. 


Problem 7

Solve problem 6 in another language you are familiar with, like C or
Java. How long did it take to write each program?