The document provides an overview of control structures in programming, detailing how statements execute sequentially and introducing conditional statements like 'if', 'else', 'elsif', and loops. It includes examples of sample programs demonstrating these control structures in action, using relational operators for comparisons. Overall, it emphasizes the importance of controlling the flow of a program based on conditions.

1. CONTROL STRUCTURES

2. Control Structures
A program is a collection of statements. After the program
executes one statement, it "moves" to the next statement and
executes that one.
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 and for…each.
1. if

4. Flow of Control – ‘if’

5. Flow of Control – ‘if-else’

6. The condition in an if statement can be any expression.
The condition is usually one that is built from relational or
logical operators.
For example,
$x > $y
is a condition that is true if the value of $x is greater than the
value of $y
Relational Operators: operators that compare 2 expressions

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 linen";
$a = <STDIN>;
$b = <STDIN>;
if
( $a < $b ) {
print "$a then $bn";
}
else
{
print "$b then $an";
}

12. elsif

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