Loop Exits and Structured Programming: Reopening the Debate Eric S
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Chapter 4 Programming in Perl
Chapter 4 Programming in Perl 4.1 More on built-in functions in Perl There are many built-in functions in Perl, and even more are available as modules (see section 4.4) that can be downloaded from various Internet places. Some built-in functions have already been used in chapter 3.1 and some of these and some others will be described in more detail here. 4.1.1 split and join (+ qw, x operator, \here docs", .=) 1 #!/usr/bin/perl 2 3 $sequence = ">|SP:Q62671|RATTUS NORVEGICUS|"; 4 5 @parts = split '\|', $sequence; 6 for ( $i = 0; $i < @parts; $i++ ) { 7 print "Substring $i: $parts[$i]\n"; 8 } • split is used to split a string into an array of substrings. The program above will write out Substring 0: > Substring 1: SP:Q62671 Substring 2: RATTUS NORVEGICUS • The first argument of split specifies a regular expression, while the second is the string to be split. • The string is scanned for occurrences of the regexp which are taken to be the boundaries between the sub-strings. 57 58 CHAPTER 4. PROGRAMMING IN PERL • The parts of the string which are matched with the regexp are not included in the substrings. • Also empty substrings are extracted. Note, however that trailing empty strings are removed by default. • Note that the | character needs to be escaped in the example above, since it is a special character in a regexp. • split returns an array and since an array can be assigned to a list we can write: splitfasta.ply 1 #!/usr/bin/perl 2 3 $sequence=">|SP:Q62671|RATTUS NORVEGICUS|"; 4 5 ($marker, $code, $species) = split '\|', $sequence; 6 ($dummy, $acc) = split ':', $code; 7 print "This FastA sequence comes from the species $species\n"; 8 print "and has accession number $acc.\n"; splitfasta.ply • It is not uncommon that we want to write out long pieces of text using many print statements. -
1. Introduction to Structured Programming 2. Functions
UNIT -3Syllabus: Introduction to structured programming, Functions – basics, user defined functions, inter functions communication, Standard functions, Storage classes- auto, register, static, extern,scope rules, arrays to functions, recursive functions, example C programs. String – Basic concepts, String Input / Output functions, arrays of strings, string handling functions, strings to functions, C programming examples. 1. Introduction to structured programming Software engineering is a discipline that is concerned with the construction of robust and reliable computer programs. Just as civil engineers use tried and tested methods for the construction of buildings, software engineers use accepted methods for analyzing a problem to be solved, a blueprint or plan for the design of the solution and a construction method that minimizes the risk of error. The structured programming approach to program design was based on the following method. i. To solve a large problem, break the problem into several pieces and work on each piece separately. ii. To solve each piece, treat it as a new problem that can itself be broken down into smaller problems; iii. Repeat the process with each new piece until each can be solved directly, without further decomposition. 2. Functions - Basics In programming, a function is a segment that groups code to perform a specific task. A C program has at least one function main().Without main() function, there is technically no C program. Types of C functions There are two types of functions in C programming: 1. Library functions 2. User defined functions 1 Library functions Library functions are the in-built function in C programming system. For example: main() - The execution of every C program starts form this main() function. -
7. Control Flow First?
Copyright (C) R.A. van Engelen, FSU Department of Computer Science, 2000-2004 Ordering Program Execution: What is Done 7. Control Flow First? Overview Categories for specifying ordering in programming languages: Expressions 1. Sequencing: the execution of statements and evaluation of Evaluation order expressions is usually in the order in which they appear in a Assignments program text Structured and unstructured flow constructs 2. Selection (or alternation): a run-time condition determines the Goto's choice among two or more statements or expressions Sequencing 3. Iteration: a statement is repeated a number of times or until a Selection run-time condition is met Iteration and iterators 4. Procedural abstraction: subroutines encapsulate collections of Recursion statements and subroutine calls can be treated as single Nondeterminacy statements 5. Recursion: subroutines which call themselves directly or indirectly to solve a problem, where the problem is typically defined in terms of simpler versions of itself 6. Concurrency: two or more program fragments executed in parallel, either on separate processors or interleaved on a single processor Note: Study Chapter 6 of the textbook except Section 7. Nondeterminacy: the execution order among alternative 6.6.2. constructs is deliberately left unspecified, indicating that any alternative will lead to a correct result Expression Syntax Expression Evaluation Ordering: Precedence An expression consists of and Associativity An atomic object, e.g. number or variable The use of infix, prefix, and postfix notation leads to ambiguity An operator applied to a collection of operands (or as to what is an operand of what arguments) which are expressions Fortran example: a+b*c**d**e/f Common syntactic forms for operators: The choice among alternative evaluation orders depends on Function call notation, e.g. -
Structured Programming - Retrospect and Prospect Harlan D
University of Tennessee, Knoxville Trace: Tennessee Research and Creative Exchange The aH rlan D. Mills Collection Science Alliance 11-1986 Structured Programming - Retrospect and Prospect Harlan D. Mills Follow this and additional works at: http://trace.tennessee.edu/utk_harlan Part of the Software Engineering Commons Recommended Citation Mills, Harlan D., "Structured Programming - Retrospect and Prospect" (1986). The Harlan D. Mills Collection. http://trace.tennessee.edu/utk_harlan/20 This Article is brought to you for free and open access by the Science Alliance at Trace: Tennessee Research and Creative Exchange. It has been accepted for inclusion in The aH rlan D. Mills Collection by an authorized administrator of Trace: Tennessee Research and Creative Exchange. For more information, please contact [email protected]. mJNDAMNTL9JNNEPTS IN SOFTWARE ENGINEERING Structured Programming. Retrospect and Prospect Harlan D. Mills, IBM Corp. Stnuctured program- 2 ' dsger W. Dijkstra's 1969 "Struc- mon wisdom that no sizable program Ste red .tured Programming" articlel could be error-free. After, many sizable ming haxs changed ho w precipitated a decade of intense programs have run a year or more with no programs are written focus on programming techniques that has errors detected. since its introduction fundamentally alteredhumanexpectations and achievements in software devel- Impact of structured programming. two decades ago. opment. These expectations and achievements are However, it still has a Before this decade of intense focus, pro- not universal because of the inertia of lot of potentialfor gramming was regarded as a private, industrial practices. But they are well- lot of fo puzzle-solving activity ofwriting computer enough established to herald fundamental more change. -
Eloquent Javascript © 2011 by Marijn Haverbeke Here, Square Is the Name of the Function
2 FUNCTIONS We have already used several functions in the previous chapter—things such as alert and print—to order the machine to perform a specific operation. In this chap- ter, we will start creating our own functions, making it possible to extend the vocabulary that we have avail- able. In a way, this resembles defining our own words inside a story we are writing to increase our expressive- ness. Although such a thing is considered rather bad style in prose, in programming it is indispensable. The Anatomy of a Function Definition In its most basic form, a function definition looks like this: function square(x) { return x * x; } square(12); ! 144 Eloquent JavaScript © 2011 by Marijn Haverbeke Here, square is the name of the function. x is the name of its (first and only) argument. return x * x; is the body of the function. The keyword function is always used when creating a new function. When it is followed by a variable name, the new function will be stored under this name. After the name comes a list of argument names and finally the body of the function. Unlike those around the body of while loops or if state- ments, the braces around a function body are obligatory. The keyword return, followed by an expression, is used to determine the value the function returns. When control comes across a return statement, it immediately jumps out of the current function and gives the returned value to the code that called the function. A return statement without an expres- sion after it will cause the function to return undefined. -
Control Flow, Functions
UNIT III CONTROL FLOW, FUNCTIONS 9 Conditionals: Boolean values and operators, conditional (if), alternative (if-else), chained conditional (if-elif-else); Iteration: state, while, for, break, continue, pass; Fruitful functions: return values, parameters, local and global scope, function composition, recursion; Strings: string slices, immutability, string functions and methods, string module; Lists as arrays. Illustrative programs: square root, gcd, exponentiation, sum an array of numbers, linear search, binary search. UNIT 3 Conditionals: Boolean values: Boolean values are the two constant objects False and True. They are used to represent truth values (although other values can also be considered false or true). In numeric contexts (for example when used as the argument to an arithmetic operator), they behave like the integers 0 and 1, respectively. A string in Python can be tested for truth value. The return type will be in Boolean value (True or False) To see what the return value (True or False) will be, simply print it out. str="Hello World" print str.isalnum() #False #check if all char are numbers print str.isalpha() #False #check if all char in the string are alphabetic print str.isdigit() #False #test if string contains digits print str.istitle() #True #test if string contains title words print str.isupper() #False #test if string contains upper case print str.islower() #False #test if string contains lower case print str.isspace() #False #test if string contains spaces print str.endswith('d') #True #test if string endswith a d print str.startswith('H') #True #test if string startswith H The if statement Conditional statements give us this ability to check the conditions. -
The Return Statement a More Complex Example
We Write Programs to Do Things Anatomy of a Function Definition • Functions are the key doers name parameters Function Call Function Definition def plus(n): Function Header """Returns the number n+1 Docstring • Command to do the function • Defines what function does Specification >>> plus(23) Function def plus(n): Parameter n: number to add to 24 Header return n+1 Function Precondition: n is a number""" Body >>> (indented) x = n+1 Statements to execute when called return x • Parameter: variable that is listed within the parentheses of a method header. The vertical line Use vertical lines when you write Python indicates indentation on exams so we can see indentation • Argument: a value to assign to the method parameter when it is called The return Statement A More Complex Example • Format: return <expression> Function Definition Function Call § Used to evaluate function call (as an expression) def foo(a,b): >>> x = 2 § Also stops executing the function! x ? """Return something >>> foo(3,4) § Any statements after a return are ignored Param a: number • Example: temperature converter function What is in the box? Param b: number""" def to_centigrade(x): x = a A: 2 """Returns: x converted to centigrade""" B: 3 y = b C: 16 return 5*(x-32)/9.0 return x*y+y D: Nothing! E: I do not know Understanding How Functions Work Text (Section 3.10) vs. Class • Function Frame: Representation of function call Textbook This Class • A conceptual model of Python to_centigrade 1 Draw parameters • Number of statement in the as variables function body to execute next to_centigrade x –> 50.0 (named boxes) • Starts with 1 x 50.0 function name instruction counter parameters Definition: Call: to_centigrade(50.0) local variables (later in lecture) def to_centigrade(x): return 5*(x-32)/9.0 1 Example: to_centigrade(50.0) Example: to_centigrade(50.0) 1. -
Edsger W. Dijkstra: a Commemoration
Edsger W. Dijkstra: a Commemoration Krzysztof R. Apt1 and Tony Hoare2 (editors) 1 CWI, Amsterdam, The Netherlands and MIMUW, University of Warsaw, Poland 2 Department of Computer Science and Technology, University of Cambridge and Microsoft Research Ltd, Cambridge, UK Abstract This article is a multiauthored portrait of Edsger Wybe Dijkstra that consists of testimo- nials written by several friends, colleagues, and students of his. It provides unique insights into his personality, working style and habits, and his influence on other computer scientists, as a researcher, teacher, and mentor. Contents Preface 3 Tony Hoare 4 Donald Knuth 9 Christian Lengauer 11 K. Mani Chandy 13 Eric C.R. Hehner 15 Mark Scheevel 17 Krzysztof R. Apt 18 arXiv:2104.03392v1 [cs.GL] 7 Apr 2021 Niklaus Wirth 20 Lex Bijlsma 23 Manfred Broy 24 David Gries 26 Ted Herman 28 Alain J. Martin 29 J Strother Moore 31 Vladimir Lifschitz 33 Wim H. Hesselink 34 1 Hamilton Richards 36 Ken Calvert 38 David Naumann 40 David Turner 42 J.R. Rao 44 Jayadev Misra 47 Rajeev Joshi 50 Maarten van Emden 52 Two Tuesday Afternoon Clubs 54 2 Preface Edsger Dijkstra was perhaps the best known, and certainly the most discussed, computer scientist of the seventies and eighties. We both knew Dijkstra |though each of us in different ways| and we both were aware that his influence on computer science was not limited to his pioneering software projects and research articles. He interacted with his colleagues by way of numerous discussions, extensive letter correspondence, and hundreds of so-called EWD reports that he used to send to a select group of researchers. -
Graceful Language Extensions and Interfaces
Graceful Language Extensions and Interfaces by Michael Homer A thesis submitted to the Victoria University of Wellington in fulfilment of the requirements for the degree of Doctor of Philosophy Victoria University of Wellington 2014 Abstract Grace is a programming language under development aimed at ed- ucation. Grace is object-oriented, imperative, and block-structured, and intended for use in first- and second-year object-oriented programming courses. We present a number of language features we have designed for Grace and implemented in our self-hosted compiler. We describe the design of a pattern-matching system with object-oriented structure and minimal extension to the language. We give a design for an object-based module system, which we use to build dialects, a means of extending and restricting the language available to the programmer, and of implementing domain-specific languages. We show a visual programming interface that melds visual editing (à la Scratch) with textual editing, and that uses our dialect system, and we give the results of a user experiment we performed to evaluate the usability of our interface. ii ii Acknowledgments The author wishes to acknowledge: • James Noble and David Pearce, his supervisors; • Andrew P. Black and Kim B. Bruce, the other designers of Grace; • Timothy Jones, a coauthor on a paper forming part of this thesis and contributor to Minigrace; • Amy Ruskin, Richard Yannow, and Jameson McCowan, coauthors on other papers; • Daniel Gibbs, Jan Larres, Scott Weston, Bart Jacobs, Charlie Paucard, and Alex Sandilands, other contributors to Minigrace; • Gilad Bracha, Matthias Felleisen, and the other (anonymous) review- ers of papers forming part of this thesis; • the participants in his user study; • David Streader, John Grundy, and Laurence Tratt, examiners of the thesis; • and Alexandra Donnison, Amy Chard, Juanri Barnard, Roma Kla- paukh, and Timothy Jones, for providing feedback on drafts of this thesis. -
Subroutines – Get Efficient
Subroutines – get efficient So far: The code we have looked at so far has been sequential: Subroutines – getting efficient with Perl do this; do that; now do something; finish; Problem Bela Tiwari You need something to be done over and over, perhaps slightly [email protected] differently depending on the context Solution Environmental Genomics Thematic Programme Put the code in a subroutine and call the subroutine whenever needed. Data Centre http://envgen.nox.ac.uk Syntax: There are a number of correct ways you can define and use Subroutines – get efficient subroutines. One is: A subroutine is a named block of code that can be executed as many times #!/usr/bin/perl as you wish. some code here; some more here; An artificial example: lalala(); #declare and call the subroutine Instead of: a bit more code here; print “Hello everyone!”; exit(); #explicitly exit the program ############ You could use: sub lalala { #define the subroutine sub hello_sub { print "Hello everyone!\n“; } #subroutine definition code to define what lalala does; #code defining the functionality of lalala more defining lalala; &hello_sub; #call the subroutine return(); #end of subroutine – return to the program } Syntax: Outline review of previous slide: Subroutines – get efficient Syntax: #!/usr/bin/perl Permutations on the theme: lalala(); #call the subroutine Defining the whole subroutine within the script when it is first needed: sub hello_sub {print “Hello everyone\n”;} ########### sub lalala { #define the subroutine The use of an ampersand to call the subroutine: &hello_sub; return(); #end of subroutine – return to the program } Note: There are subtle differences in the syntax allowed and required by Perl depending on how you declare/define/call your subroutines. -
A Comparative Analysis of Structured and Object-Oriented Programming Methods
JASEM ISSN 1119-8362 Full-text Available Online at J. Appl. Sci. Environ. Manage. December, 2008 All rights reserved www.bioline.org.br/ja Vol. 12(4) 41 - 46 A Comparative Analysis of Structured and Object-Oriented Programming Methods ASAGBA, PRINCE OGHENEKARO; OGHENEOVO, EDWARD E. CPN, MNCS. Department of Computer Science, University of Port Harcourt, Port Harcourt, Nigeria. [email protected], [email protected]. 08056023566 ABSTRACT: The concepts of structured and object-oriented programming methods are not relatively new but these approaches are still very much useful and relevant in today’s programming paradigm. In this paper, we distinguish the features of structured programs from that of object oriented programs. Structured programming is a method of organizing and coding programs that can provide easy understanding and modification, whereas object- oriented programming (OOP) consists of a set of objects, which can vary dynamically, and which can execute by acting and reacting to each other, in much the same way that a real-world process proceeds (the interaction of real- world objects). An object-oriented approach makes programs more intuitive to design, faster to develop, more amenable to modifications, and easier to understand. With the traditional, procedural-oriented/structured programming, a program describes a series of steps to be performed (an algorithm). In the object-oriented view of programming, instead of programs consisting of sets of data loosely coupled to many different procedures, object- oriented programs -
PHP: Constructs and Variables Introduction This Document Describes: 1
PHP: Constructs and Variables Introduction This document describes: 1. the syntax and types of variables, 2. PHP control structures (i.e., conditionals and loops), 3. mixed-mode processing, 4. how to use one script from within another, 5. how to define and use functions, 6. global variables in PHP, 7. special cases for variable types, 8. variable variables, 9. global variables unique to PHP, 10. constants in PHP, 11. arrays (indexed and associative), Brief overview of variables The syntax for PHP variables is similar to C and most other programming languages. There are three primary differences: 1. Variable names must be preceded by a dollar sign ($). 2. Variables do not need to be declared before being used. 3. Variables are dynamically typed, so you do not need to specify the type (e.g., int, float, etc.). Here are the fundamental variable types, which will be covered in more detail later in this document: • Numeric 31 o integer. Integers (±2 ); values outside this range are converted to floating-point. o float. Floating-point numbers. o boolean. true or false; PHP internally resolves these to 1 (one) and 0 (zero) respectively. Also as in C, 0 (zero) is false and anything else is true. • string. String of characters. • array. An array of values, possibly other arrays. Arrays can be indexed or associative (i.e., a hash map). • object. Similar to a class in C++ or Java. (NOTE: Object-oriented PHP programming will not be covered in this course.) • resource. A handle to something that is not PHP data (e.g., image data, database query result).