TYPES OF CONTROL STRUCTURES SEEN IN PERL.ppt

Control structures in perl

1. CONTROL STRUCTURES

2. Control Structures
Aprogramisacollectionofstatements.Aftertheprogram
executesonestatement,it"moves"tothenextstatementand
executesthatone.
The execution flow is a simple sequence.
Example:
$number1 = ‘ATCG’;
$number2 = ‘GGG’;
$sum = $number1.$number2;
Print $num;
Output: ?

3. Control structures:
if, else, elsif, switch, while, until, do…while, for andfor…each.
1. if

4. Flow of Control –‘if’

5. Flow of Control –‘if-else’

6. Theconditioninanifstatementcanbeanyexpression.
Theconditionisusuallyonethatisbuiltfromrelationalor
logicaloperators.
Forexample,
$x>$y
isaconditionthatistrueifthevalueof$xisgreaterthanthe
valueof$y
RelationalOperators:operatorsthatcompare2expressions

7. Numeric relational operators

8. Comparing Strings

10. 1. Sample Program using ‘if’ and ‘if else’
$sequence="ATGC";
if(defined $seq)
{
print "defined";
}
else
{
print "not defined";
}
Output: ???

11. 2. Sample Program using ‘if’ and ‘if else’
print "Enter 2 numbers, one per line\n";
$a = <STDIN>;
$b = <STDIN>;
if
( $a < $b ) {
print "$a then $b\n";
}
else
{
print "$b then $a\n";
}

12. elsif

14. print "Enter 2 numbers, one per line\n";
$a = <STDIN>;
$b = <STDIN>;
if
( $a < $b ) {
print "$a is less than $b\n";
}
elsif
( $b < $a ) {
print "$b is less than $a\n";
}
else
{
print "The numbers are equal.\n";
}
1. Sample program using ‘elsif’