scalar expressions and perl program on them

1. SCALAR EXPRESSIONS
 Scalar data items are combined into expressions using operators.
$c=12;
$d=3+($c);
 1) ARITHMETIC OPERATORS
Perl provides usual arithmetic operator including auto-increment and auto-decrement.
Operator Example Result Definition
+ 7 + 7 = 14 Addition
- 7 - 7 = 0 Subtraction
* 7 * 7 = 49 Multiplication
/ 7 / 7 = 1 Division
** 7 ** 7 = 823543 Exponents
% 7 % 7 = 0 Modulus
$c=17;
$d=++$c; //increment then assign
$c=12;
$d=$c ++; //assign then increment
Binary arithmetic operation:
$a+=3;
$a=a+3;

2.  2)String Operators
In Perl most of the processing is done by using built-in functions
and regular expressions.
 Perl uses period (.) for concatenation of strings
 The other string operator is (x), used to replicate strings.
$a=“hello” x 3
$a=“hellohellohello”
$foo.= “ ”
 Arithmetic Operators used in String Context.
1. Auto-increment
This operator can be applied to a variable.
If a variable is assigned with string of letters and digits then auto
increment operation is applied on the string from rightmost character.
eg: $a=‘all12’;
print ++$a;
result: bmm23
2. Unary minus
If this is applied to string which starts with a plus or minus character,
then it returns the same string with opposite sign.
eg. $name=“sia”
-$name=“-sia”

3.  3) Comparison operator
Values of comparison is returned in numbers.
1--- if true and (“ ”) – if false
These are classified into two kinds. One for numbers and other for strings.
 Numbers: ==,!=,<,>,<=,>=,<=>(comparison operator)
 Strings: eq,ne,lt,gt,le,ge,cmp
 4)Logical operator
not ---- !
and ---- &&
or ---- ||
print “OKn” if $a<10 and $b<12;
 5) Conditional expressions
it is the one whose value is chosen from one of the alternatives at runtime
depending on the outcome of test.
test? True_exp:false_exp
eg: $a=($a<0)?0:$a;

4. CONTROL STRUCTURES
 A control structure is a block of programming that analyzes variables and chooses a
direction in which to go based on given parameters. The term flow control details the
direction the program takes (which way program control "flows").
 Blocks: It is a sequence of one or more statements enclosed in curly braces.
eg: {
$positive=1;
$negative=-1;
}
 Conditions: They make use of relational operators. It is a Perl expression which is
evaluated in Boolean context.
 If it evaluates to --- 0 or (“ “) --- condition is false, else it is treated as true.
 $total > 50 and $total <100
 A condition can be negated using ! Operator, we can specify that as
!($total > 50 and $total<100)

5. CONDITIONAL EXPRESSIONS
 Conditional Expressions should be in brackets.
 If-then-else statement:
if($total> 0){
print “$totaln”
} else {
print “wrong total ! n”
}
 If-elsif statement
if($total> 70) { $grade=“A”;} elsif($total > 56){ $grade =“B”;} else
{$grade=“C”); }
 Alternative to if-then-else statements are ‘conditional expression’ and using ‘or’
operator.
 In perl a single statement can be followed by a conditional modifier.
print “OKn” if $volts>=1.5;

6. REPETITION
 Testing loops and counting loops can be used for repetition mechanisms.
 Testing loops: while($a!=$b){
if($a > $b){
$a=$a-$b;
}else {
$b=$b-$a;
}
}
 An until loop statement in Perl programming language repeatedly executes a target
statement as long as a given condition is false.
 Syntax
 The syntax of an until loop in Perl programming language is −
 until(condition) { statement(s); }
 Here statement(s) may be a single statement or a block of statements.
 The condition may be any expression. The loop iterates until the condition becomes
true.
 When the condition becomes true, the program control passes to the line immediately
following the loop.
 $a+=2 while $a < $b; (and) $a+=2 until $a < $b;
 Although condition is specified after the written statement, it is evaluated before the
statement executed.

7.  Do loop:
It is built-in function rather than a syntactic construct.Overhere the condition is tested after
the execution of the block, so the block is executed at least once.
do{
...
}while $a!=$b;
 Counting Loops: They use same syntax as c
for($i=1;$i<=10;$i++){
$i_square=$i*$i;
$i_cube=$i**3;
print “ $it$i_squaret$i_cuben”;
}
 foreach $i (1..10) {
$i_square=$i*$i; $i_cube=$i**3;
print “ $it$i_squaret$i_cuben”; }

8. LOOP REFINEMENTS
 Perl provides three loop commands : last , next and redo . The last and next
command are similar to break and continue statements in c language.
 last breaks out of the loop and next forces the next iteration of a loop.
 Ex: to terminate input processing if a line contains ‘quit’ is read we write
while <STDIN> {
last if /quit/;
...
}
 The redo command repeats the current iteration from the beginning.
Output:
3 4 5 6 7