Category:Articles with example Perl code
Pages in category "Articles with example Perl code"
The following 24 pages are in this category, out of 24 total, this list may not reflect recent changes (learn more).
The following 24 pages are in this category, out of 24 total, this list may not reflect recent changes (learn more).
1. Comment (computer programming) – In computer programming, a comment is a programmer-readable explanation or annotation in the source code of a computer program. They are added with the purpose of making the code easier for humans to understand. The syntax of comments in various programming languages varies considerably, the flexibility provided by comments allows for a wide degree of variability, but formal conventions for their use are commonly part of programming style guides. Comments are generally formatted as either block comments or line comments, block comments delimit a region of source code which may span multiple lines. This region is specified with a start delimiter and an end delimiter, some programming languages allow block comments to be recursively nested inside one another, but others do not. Line comments either start with a comment delimiter and continue until the end of the line, or in cases, start at a specific column in the source code. Some programming languages employ both block and line comments with different comment delimiters, for example, C++ has block comments delimited by /* and */ that can span multiple lines and line comments delimited by //. Other languages support only one type of comment, for example, Ada comments are line comments, they start with -- and continue to the end of the line. How best to use of comments is subject to dispute, different commentators have offered varied. There are many different ways of writing comments and many commentators who offer sometimes conflicting advice, Comments can be used as a form of pseudocode to outline intention prior to writing the actual code. In this case it should explain the logic behind the code rather than the code itself, if this type of comment is left in, it simplifies the review process by allowing a direct comparison of the code with the intended results. A common logical fallacy is that code that is easy to understand does what its supposed to do, Comments can be used to summarize code or to explain the programmers intent. Dont document bad code – rewrite it, Good comments dont repeat the code or explain it. Comments should explain, at a level of abstraction than the code. Comments may also be used to explain why a block of code does not seem to fit conventions or best practices and this is especially true of projects involving very little development time, or in bug fixing. For example, Sometimes source code contains a novel or noteworthy solution to a specific problem, in such cases, comments may contain an explanation of the methodology. Such explanations may include diagrams and formal mathematical proofs and this may constitute explanation of the code, rather than a clarification of its intent, but others tasked with maintaining the code base may find such explanation crucial. This might especially be true in the case of highly specialized problem domains, or rarely used optimizations, constructs or function-calls
2. Do while loop – The do while construct consists of a process symbol and a condition. First, the code within the block is executed, and then the condition is evaluated, if the condition is true the code within the block is executed again. This repeats until the condition becomes false, because do while loops check the condition after the block is executed, the control structure is often also known as a post-test loop. Contrast with the loop, which tests the condition before the code within the block is executed. This means that the code must always be executed first and then the expression or test condition is evaluated, if it is true, the code executes the body of the loop again. This process is repeated as long as the expression evaluates to true, if the expression is false, the loop terminates and control transfers to the statement following the do-while loop. It is possible, and in some cases desirable, for the condition to always evaluate to true, when such a loop is created intentionally, there is usually another control structure that allows termination of the loop. Some languages may use a different naming convention for this type of loop, for example, the Pascal language has a repeat until loop, which continues to run until the control expression is true — whereas a while loop runs while the control expression is true. Is equivalent to In this manner, the do, while loop saves the initial loop priming with do_work, on the line before the while loop. Early BASICs used the syntax WHILE/WEND, modern BASICs such as PowerBASIC provide both WHILE/WEND and DO/LOOP structures, with syntax such as DO WHILE/LOOP, DO UNTIL/LOOP, DO/LOOP WHILE, DO/LOOP UNTIL, and DO/LOOP. The PL/I DO statement subsumes the functions of the post-test loop, the pre-test loop, all functions can be included in a single statement. The example shows only the do until syntax, declare counter fixed initial, declare factorial fixed initial, do until, factorial = factorial * counter, counter = counter -1, end, put, Python lacks a specific do while flow control construct. However, the equivalent may be constructed out of a loop with a break. In Racket, as in other Scheme implementations, a named-let is a way to implement loops. Be aware that a named let can also take arguments, Racket and Scheme also provide a proper do loop. Swift 2. x, Swift 1. x, Control flow For loop Foreach While loop Repeat loop do while in C macros
3. For loop – In computer science, a for-loop is a control flow statement for specifying iteration, which allows code to be executed repeatedly. g. Descendants of ALGOL use for, while descendants of Fortran use do, there are other possibilities, for example COBOL which uses PERFORM VARYING. Unlike many other kinds of loops, such as the while-loop and this allows the body of the for-loop to know about the sequencing of each iteration. For-loops are also used when the number of iterations is known before entering the loop. For-loops are the way to make loops when the number of iterations is known. The name for-loop comes from the English word for, which is used as the keyword in most programming languages to introduce a for-loop. In FORTRAN and PL/I though, the keyword DO is used and it is called a do-loop, a for-loop statement is available in most imperative programming languages. Even ignoring minor differences in syntax there are differences in how these statements work. An optional step-value may also be included, although the exact syntaxes used for this differs a bit more between the languages, some languages require a separate declaration of the control variable, some do not. Another form was popularized by the C programming language and it requires 3 parts, the initialization, the condition, and the afterthought and all these three parts are optional. The initialization declares any variables required, the type of a variable should be same if you are using multiple variables in initialization part. The condition checks a condition, and quits the loop if false, the afterthought is performed exactly once every time the loop ends and then repeats. Here is an example of the traditional for-loop in Java and this type of for-loop is a generalisation of the numeric range type of for-loop, as it allows for the enumeration of sets of items other than number sequences. It is usually characterized by the use of an implicit or explicit iterator, a representative example in Python is, Where some_iterable_object is either a data collection that supports implicit iteration, or may in fact be an iterator itself. Some languages have this in addition to another for-loop syntax, notably, PHP has this type of loop under the name for each, some languages also offer array assignment statements, that enable many for-loops to be omitted. Thus pseudocode such as A, =0, would set all elements of array A to zero, no matter its size or dimensionality. The example loop could be rendered as But whether that would be rendered in the style of the for-loop or the for all-loop or something else may not be described in the compiler manual. Introduced with ALGOL68 and followed by PL/I, this allows the iteration of a loop to be compounded with a test and that is, a value is assigned to the loop variable i and only if the while expression is true will the loop body be executed
4. Perl 6 – Perl 6 is a member of the Perl family of programming languages. While historically several interpreter and compiler implementations were being written, today only the Rakudo Perl implementation is in active development and it is introducing elements of many modern and historical languages. Compatibility with Perl 5 is not a goal, though a compatibility mode is part of the specification, the design process for Perl 6 began in 2000. Development on Pugs, the first high-traction implementation, began in 2005, Larry Wall maintains a reference grammar known as STD. pm6, written in Perl 6 and bootstrapped with Perl 5. The Perl 6 design process was first announced on July 19,2000, on the day of that years Perl Conference. The process began with a series of requests for comments or RFCs and this process was open to all contributors, and left no aspect of the language closed to change. Once the RFC process was complete, Wall reviewed and classified each request and he then began the process of writing several Apocalypses, a term which means revealing. For this reason, a set of Synopses were published, each one relating the contents of an Apocalypse, today, Perl 6 specification continues almost entirely within the Synopses. There are also a series of Exegeses written by Damian Conway that explain the content of each Apocalypse in terms of practical usage, each Exegesis consists of code examples along with discussion of the usage and implications of the examples. There are three methods of communication used in the development of Perl 6 today. The first is the #perl6 connect IRC channel on freenode, the second is a set of mailing lists on The Perl Foundations servers at perl. org. The third is the Git source code repository hosted at https, the break in compatibility was mandated from the start of the project, and immediately allowed some of the changes that Larry Wall had suggested in his initial speech. Over the years, Perl 6 has undergone several alterations in its direction, the languages mascot is Camelia, the Perl 6 bug. Her name is a nod to the camel mascot associated with Perl, spiral designs embedded in her butterfly-like wings resemble the characters P6, the favored nickname for Perl 6. As of 2015, only the Rakudo Perl implementation is under active development, no implementation will be designated as the official Perl 6 implementation, rather, Perl 6 is anything that passes the official test suite. Rakudo Perl targets a number of machines, such as MoarVM. MoarVM is a machine designed for gradually typed programming languages. Large portions of Rakudo are written in Perl 6 itself, or in its subset NQP, Rakudo is not a completely self-hosting implementation, nor are there concrete plans at this point to make Rakudo a bootstrapping compiler
5. While loop – In most computer programming languages, a while loop is a control flow statement that allows code to be executed repeatedly based on a given Boolean condition. The while loop can be thought of as an if statement. The while construct consists of a block of code and a condition/expression, the condition/expression is evaluated, and if the condition/expression is true, the code within the block is executed. This repeats until the condition/expression becomes false, because the while loop checks the condition/expression before the block is executed, the control structure is often also known as a pre-test loop. Compare this with the do loop, which tests the condition/expression after the loop has executed. For example, in the C programming language, the code fragment first checks whether x is less than 5, which it is, so then the is entered, where the printf function is run and x is incremented by 1. After completing all the statements in the body, the condition, is checked again, and the loop is executed again. Note that it is possible, and in some cases desirable, for the condition to always evaluate to true, when such a loop is created intentionally, there is usually another control structure that controls termination of the loop. Also, in C and its descendants, a loop is a for loop with no initialization or counting expressions, i. e. Smalltalk also has a corresponding whileFalse. Do while loop For loop Foreach LOOP – a programming language with the property that the functions it can compute are exactly the primitive recursive functions