IT441 Network Services Administration

1. IT441Network Services Administration Prof. Alfred J Bird, Ph.D., NBCT abird@cs.umb.edu http://it441-s14-bird.wikispaces.umb.edu/ Door Code for IT441 Students – 536587* Office – McCormick 3rd floor 607 Office Hours – Tuesday and Thursday 4:00pm to 5:15pm

2. Ways to get out of a program • exit (0); • die $string;

3. Increment/Decrement • A very helpful construct is the increment/decrement statement • $i++ is equivalent to $i = $i+1 • $j = $i++ • $j = ++$i • $j = $i - - • $j = - - $i

4. Arithmetic Comparisons • $x > $y • $x < $y • $x >= $y • $x < =$y • $x == $y • $x != $y

5. String Comparisions • $x gt $y • $x lt $y • $x ge $y • $x le $y • $x eq $y • $x ne $y

6. Logical Operators • $x and &y • $x && $y • $x or $y • $x || $y • not $x • !$x

7. Control Flow Constructs • What is a control statement? • Types of control statements: • if • while • for

8. If Statements • if • if ( condition ) { action } • if else • if (condition ) { action } • else {another action } • if elsif else • if ( condition ) { action } • elsif (another condition ) { another action } • … • else { a further action }

9. If Statements Practice • Write a short program to: • Read in a number • Test if it is zero, even or odd • Print out the result

10. If Statements (cont) • unless statement unless (condition) {action}; • Reversed order print “Hello Al\n” if($inputName = “Al”); die “Can’t divide by zero\n:” if ($num4 == 0);

11. While Statement • while loops • while ( condition ) { action } • $i=1; • while ($i<=5) { • print $i, “\n”; • $i++; • } • until loops • Same form but opposite action of the while loop

12. While Statement Exercise • Write a short program using a while loop to: • Print out the integers from -5 to 5 • Modify the program to use an until loop

13. An interesting variable • $_ is the default variable for many functions • while ( $line = <STDIN>) { • chomp ($line); • … • } • while (<STDIN>) { • chomp; • … • }

14. Breaking Out of a Loop • There are three ways to modify the execution of the loop: • last; • next; • redo; • Statement labels • Labels a location in the program • Best to use all uppercase letters OUTER: while(…) { … }

15. Another Form of Loops • do { action } while ( condition ); • do { action } until ( condition );

16. For statement • for loop • for ( init_exp ; test_exp; step_exp) { action } • for ($i=1; $i<5; $i++) {print $i, “\n”;}

17. Foreach loop • foreach my $number (1..10) { • print “The number is: $number \n”; • }

18. For next time • Read Chapter 3 “Control Flow Constructs” pp 53-79 • Exercises 1, 2 & 3 on page 79