How to Repeat a for Loop Again From Within Loop Perl

Summary: in this tutorial, we will show how to use the Perl for loop argument to loop over elements of a list.

Perl for and foreach statements

The Perl for loop statement allows you to loop over elements of a listing. In each iteration, you tin procedure each element of the list separately. This is why the for loop statement is sometimes referred to as foreach loop.

In Perl, the for and foreach loop are interchangeable, therefore, you can use the foreach keyword in where you use the for keyword.

The flowchart of the Perl for loop is every bit follows:

Perl for loop example

The following example uses the Perl for loop argument to loop over elements of an array:

            
                              #!/usr/bin/perl                use                warnings;                use                strict;                my                @a = (ane..nine);                for(@a){                print("$_","\north"); }            
                          Lawmaking linguistic communication:              Perl              (              perl              )                      

How information technology works.

• Beginning, we defined an array of 9 integers@a
• 2nd, nosotros used for loop statement to loop over elements of the @a assortment.
• Tertiary, inside the loop, we displayed element's value using default variable $_. We hash out the default variable $_ in the adjacent section.

If you replace the for keyword by the foreach keyword in the above example, it works the aforementioned.

            
                              #!/usr/bin/perl                use                warnings;                use                strict;                my                @a = (1..nine);                foreach(@a){                print("$_","\north"); }            
                          Code language:              Perl              (              perl              )                      

for loop iterator

If nosotros don't supply an explicit iterator to the loop, Perl will use a special variable called default variable with the proper noun $_ as the iterator. In each iteration, Perl assigns each element of the assortment @a to the default variable $_ .

Explicit Perl for loop iterator

If you desire to specify an explicit iterator for the loop, yous can declare it in the for loop argument as follows:

            
                              #!/usr/bin/perl                use                warnings;                employ                strict;                my                @a = (i..nine);                for                my                $i (@a){                impress("$i","\north"); }            
                          Code language:              Perl              (              perl              )                      

$i is the iterator of the for loop in this example. In each iteration, Perl assigns the corresponding chemical element of the array to the $i iterator. Notice that the $i variable exists only during the execution of the loop.

If you declare an iterator earlier entering the loop, Perl will restore its original value after the loop terminated. Take a wait at the following case:

            
                              #!/usr/bin/perl                employ                warnings;                utilize                strict;                my                @a = (ane..ix);                my                $i =                xx;                for                $i (@a){                print("$i","\due north"); }                print('iterator $i is ',"$i","\n");                # 20                          
                          Code linguistic communication:              Perl              (              perl              )                      

How information technology works.

• First, we declared variable $i earlier the loop and initialized its value to 20.
• Second, we used a variable $i as the iterator; its value changes in each iteration of the loop.
• Third, afterward the loop nosotros displayed the value of $i. Perl restored its original value, which is 20.

Perl for loop iterator: value or alias

In each iteration of the loop, Perl creates an alias instead of a value. In other words, if y'all make any changes to the iterator, the changes also reflect in the elements of the array. See the following instance:

            
                              #!/usr/bin/perl                employ                warnings;                use                strict;                my                @b = (1..5);                print("Before the loop: @b \n");                for(@b){ 	$_ = $_ *                ii;  }                print("After the loop: @b \n");            
                          Code linguistic communication:              Perl              (              perl              )                      

How it works.

• First, we declared an array @b with 5 elements from 1 to v. We displayed the array @b elements using impress function.
• Second, we iterated elements of the array. We multiplied each element with 2 through the iterator $_
• 3rd, exterior of the loop, nosotros displayed the elements of the array once again

Perl C-fashion for loop

Perl also supports for loop in C-style. However, it is not a expert practise to apply the C-style for loop because to code will become less readable.

The following syntax illustrates the c-style for loop in Perl:

            
                              for                (initialization; test; step) {                //                code block; }            
                          Code language:              Perl              (              perl              )                      

There are three control parts:

• Initialization. Perl executes the initialization once when the loop is entered. We oft use initialization to initialize a loop counter variable.
• Test. Perl evaluates the exam expression at the beginning of each iteration and executes the lawmaking block within the loop torso every bit long equally the test expression evaluates to fake.
• Footstep. Perl executes step at the stop of each iteration. You often use the step to modify the loop counter.

The following flowchart illustrates the C-fashion for loop:

The following example demonstrates how to utilise C-style for loop:

            
                              #!/usr/bin/perl                utilize                warnings;                use                strict;                my                @c = (i..half dozen);                for(my                $i =                0; $i <= $#c; $i++){                print("$c[$i] \n"); }            
                          Code language:              Perl              (              perl              )                      

Hence, it is much more than readable if you Perl'south for loop manner.

            
                              #!/usr/bin/perl                use                warnings;                use                strict;                my                @c = (1..six);                for                (@c){                print("$_ \n"); }            
                          Code language:              Perl              (              perl              )                      

In this tutorial, y'all've learned about Perl for loop statement to loop over elements of a list.

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Source: https://www.perltutorial.org/perl-for-loop/

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