understanding

Save this PDF as:
 WORD  PNG  TXT  JPG

Size: px
Start display at page:

Download "understanding"

Transcription

1 understanding

2 thanks

3 welcome every single one of you

4 agenda what is nil? what is nil in Go? what does nil mean? is nil useful?

5 nil? you misspelled null

6 how I learn words

7 how I learn words

8 etymology nil Latin nihil meaning nothing null Latin ne + ullus meaning not any none Old English ne + ān meaning not one

9 names for the number zero in English - zero null duck nada zip naught aught - cipher love nil zilch the letter o nought ought source: wikipedia

10 nil is (a) zero

11 interlude a bit of history

12

13 I call it my billion-dollar mistake. It was the invention of the null reference in At that time, I was designing the first comprehensive type system for references in an object oriented language. - Sir C.A.R. Hoare

14 panic: runtime error: invalid memory address or nil pointer dereference

15 Uncaught TypeError: undefined is not a function

16

17 nil leads to panic

18 panic leads to fear by danpawley on Flickr

19 fear leads to by korymatthew on Flickr

20 λ functional programming

21 Functional Go? Thanks, but no - francesc at dotgo.eu 2015

22 there are many ways, nil is the Go way

23 </interlude>

24 zero values what are they?

25 zero values bool false pointers nil numbers 0 slices nil string "" maps nil channels nil functions nil interfaces nil

26 zero values for struct types type Person struct { AgeYears int Name string Friend []Person } var p Person // Person{0, "", nil}

27 the type of nil

28 ... unless the value is the predeclared identifier nil, which has no type - Go language specification

29 untyped zero a := false a := "" a := 0 // a := int(0) a := 0.0 // a := float64(0) a := nil // use of untyped nil

30 nil is a predeclared identifier representing the zero value for a pointer, channel, func, interface, map, or slice type. - Go documentation for builtin package

31 nil is a predeclared identifier representing the zero value for a pointer, channel, func, interface, map, or slice type. - Go documentation for builtin package

32 twenty-five* keywords break default func interface select case defer go map struct chan else goto package switch const fallthrough if range type continue for import return var * plus the five secret ones, obviously

33 predefined vs keyword // YOLO var nil = errors.new( \_(ツ)_/ ) * For extra evilness: place at the end of doc.go

34 zero values what do they mean?

35 kinds of nil pointers slices maps channels functions interfaces

36 kinds of nil pointers slices maps channels functions interfaces

37 pointers in Go - they point to a position in memory - similar to C or C++, but - no pointer arithmetic memory safety - garbage collection

38 nil pointer - points to nil a.k.a. nothing - zero value of pointers

39 kinds of nil pointers slices maps channels functions interfaces

40 slice internals []byte ptr *elem len int cap int

41 a slice with five elements []byte ptr len 5 cap 5 [5]byte s := make([]byte, 5)

42 nil slice []byte ptr nil len 0 cap 0 var s []byte

43 kinds of nil pointers slices maps channels functions interfaces

44 channels, maps, and functions ptr *something

45 channels, maps, and functions ptr implementation * implementations might not be cloud shaped

46 channels, maps, and functions ptr nil

47 kinds of nil pointers slices maps channels functions interfaces

48 (type, value)

49 var s fmt.stringer // Stringer (nil, nil) fmt.println(s == nil) // true

50 (nil, nil) equals nil

51 var p *Person // nil of type *Person var s fmt.stringer = p // Stringer (*Person, nil) fmt.println(s == nil) // false

52 (*Person, nil) doesn t equal nil

53 when is nil not nil?

54 when is nil not nil? func do() error { var err *doerror return err } // error (*doerror, nil) // nil of type *doerror func main() { err := do() fmt.println(err == nil) } // error (*doerror, nil) // false

55 do not declare concrete error vars

56 nil is not nil func do() *doerror { // nil of type *doerror return nil } func main() { err := do() fmt.println(err == nil) } // nil of type *doerror // true

57 nil is not nil func do() *doerror { return nil } // nil of type *doerror func wrapdo() error { return do() } // error (*doerror, nil) // nil of type *doerror func main() { err := wrapdo() fmt.println(err == nil) } // error (*doerror, nil) // false

58 do not return concrete error types

59 nil is not nil * for some kinds of nil

60 kinds of nil pointers point to nothing slices have no backing array maps are not initialized channels are not initialized functions are not initialized interfaces have no value assigned, not even a nil pointer

61 Make the zero value useful - Rob Pike in his Go Proverbs

62 how are these useful? pointers slices maps channels functions interfaces

63 how are these useful? pointers slices maps channels functions interfaces

64 pointers var p *int p == nil // true *p // panic: invalid memory address or nil pointer dereference

65 coding time

66 implement Sum type tree struct { v int l *tree r *tree } func (t *tree) Sum() int

67 a first solution func (t *tree) Sum() int { sum := t.v 6 if t.l!= nil { sum += t.l.sum() } if t.r!= nil { sum += t.r.sum() } return sum }

68 issues Code repetition: if v!= nil { v.m() } Panic when t is nil var t *tree sum := t.sum() // panic: invalid memory address or nil pointer dereference

69 pointer receivers type person struct {} func sayhi(p *person) { fmt.println( hi ) } func (p *person) sayhi() { fmt.println( hi ) } var p *person p.sayhi() // hi

70 nil receivers are useful 零

71 nil receivers are useful: Sum func (t *tree) Sum() int { if t == nil { return 0 } return t.v + t.l.sum() + t.r.sum() }

72 nil receivers are useful: String func (t *tree) String() string { if t == nil { return "" } return fmt.sprint(t.l, t.v, t.r) }

73 nil receivers are useful: Find func (t *tree) Find(v int) bool { if t == nil { return false } return t.v == v t.l.find(v) t.r.find(v) }

74 keep nil useful if possible, if not NewX()

75 how are these useful? pointers slices maps channels functions interfaces

76 nil slices var s []slice len(s) // 0 cap(s) // 0 for range s // iterates zero times s[i] // panic: index out of range

77 append on nil slices var s []int for i := 0; i < 10; i++ { fmt.printf("len: %2d cap: %2d\n", len(s), cap(s)) s = append(s, i) }

78 $ go run slices.go len: len: len: len: len: len: len: len: len: len: cap: 0 cap: 1 cap: 2 cap: 4 cap: 4 cap: 8 cap: 8 cap: 8 cap: 8 cap: 16 [] s is nil! [0] allocation [0 1] reallocation [0 1 2] reallocation [ ] [ ] reallocation [ ] [ ] [ ] [ ] reallocation

79 use nil slices they re often fast enough

80 how are these useful? pointers slices maps channels functions interfaces

81 nil maps var m map[t]u len(m) // 0 for range m // iterates zero times v, ok := m[i] // zero(u), false m[i] = x // panic: assignment to entry in nil map

82 using maps func NewGet(url string, headers map[string]string) (*http.request, error) { req, err := http.newrequest(http.methodget, url, nil) if err!= nil { return nil, err } for k, v := range headers { req.header.set(k, v) } return req, nil }

83 using maps NewGet( " map[string]string{ "USER_AGENT": "golang/gopher", }, )

84 $ go run request.go GET / HTTP/1.1 Host: google.com User_agent: golang/gopher

85 using empty maps NewGet(" map[string]string{})

86 $ go run request.go GET / HTTP/1.1 Host: google.com

87 using empty maps NewGet(" map[string]string{})

88 nil maps are valid empty maps NewGet(" nil)

89 $ go run request.go GET / HTTP/1.1 Host: google.com

90 use nil maps as read-only empty maps

91 how are these useful? pointers slices maps channels functions interfaces

92 nil channels var c chan t <- c // blocks forever c <- x // blocks forever close(c) // panic: close of nil channel

93 coding time

94 b a func merge(out chan<- int, a, b <-chan int) out

95 a naive solution func merge(out chan<- int, a, b <-chan int) { for { select { case v := <-a: out <- v case v := <-b: out <- v } } }

96 $ go run naive.go

97 closed channels var c chan t v, ok <- c // zero(t), false c <- x // panic: send on closed channel close(c) // panic: close of nil channel

98 a naive solution func merge(out chan<- int, a, b <-chan int) { for { select { case v := <-a: out <- v case v := <-b: out <- v } } }

99 checking for closed chans case v, ok := <-a: if!ok { aclosed = true continue } out <- v // analogous code for case b

100 checking for closed chans func merge(out chan<- int, a, b <-chan int) { var aclosed, bclosed bool for!aclosed!bclosed { select { case v, ok := <-a: if!ok { aclosed = true; continue } out <- v case v, ok := <-b: if!ok { bclosed = true; continue } out <- v } } }

101 $ go run checkforclosed.go fatal error: all goroutines are asleep - deadlock! goroutine 1 [chan receive]: main.main() /Users/campoy/src/github.com/campoy/talks/nil/talk/code/chans. go:97 +0x15a exit status 2

102 and closing channel out func merge(out chan<- int, a, b <-chan int) { var aclosed, bclosed bool for!aclosed!bclosed { select { case v, ok := <-a: if!ok { aclosed = true; continue } out <- v case v, ok := <-b: if!ok { bclosed = true; continue } out <- v } } close(out) }

103 and closing channel out func merge(out chan<- int, a, b <-chan int) { var aclosed, bclosed bool for!aclosed!bclosed { select { case v, ok := <-a: if!ok { aclosed = true; continue } out <- v case v, ok := <-b: if!ok { bclosed = true; continue } out <- v } } close(out) }

104 $ go run closingout.go

105 ship it! Fancy Gopher by Renee French

106 by hzeller on Flickr

107 let s log case v, ok := <-a: if!ok { aclosed = true fmt.println("a is now closed") continue } out <- v // analogous code for case b

108 $ go run withlogs.go b is now closed b is now closed 1 b is now closed b is now closed 1 a is now closed

109 let s log var aclosed, bclosed bool for!aclosed!bclosed { select { case v, ok := <-a: if!ok { aclosed = true; continue } out <- v case v, ok := <-b: if!ok { bclosed = true; continue } out <- v } } close(out)

110 can we switch off a chan?

111 nil channels var c chan t <- c // blocks forever c <- x // blocks forever close(c) // panic: close of nil channel

112 switching off a channel case v, ok := <-a: if!ok { aclosed = true fmt.println("a is now closed") continue } out <- v // analogous code for case b

113 switching off a channel case v, ok := <-a: if!ok { a = nil fmt.println("a is now closed") continue } out <- v // analogous code for case b

114 switching off a channel; no logs func merge(out chan<- int, a, b <-chan int) { for a!= nil b!= nil { select { case v, ok := <-a: if!ok { a = nil; continue } out <- v case v, ok := <-b: if!ok { b = nil; continue } out <- v } } close(out) }

115 $ go run closingout.go

116 fancy party time! Fancy Gopher by Renee French

117 use nil chans to disable a select case

118 how are these useful? pointers slices maps channels functions interfaces

119 nil funcs Go has first-class functions functions can be used as struct fields they need a zero value; logically it is nil type Foo struct { f func() error }

120 nil funcs for default values lazy initialization of variables nil can also imply default behavior func NewServer(logger func(string, interface{})) { if logger == nil { logger = log.printf } logger("initializing %s", os.getenv("hostname")) }

121 how are these useful? pointers slices maps channels functions interfaces

122 interfaces The nil interface is used as a signal if err!= nil { }

123 why does nil *Person not equal nil interface? 零

124 summer type Summer interface { func Sum() int }

125 summer var t *tree var s Summer = t fmt.println(t == nil, s.sum()) // true 0

126 summer type ints []int func (i ints) Sum() int { s := 0 for _, v := range i { s += v } return s }

127 summer var i ints var s Summer = i fmt.println(i == nil, s.sum()) // true 0

128 nil values can satisfy interfaces 零

129 nil values and default values func dosum(s Summer) int { if s == nil { return 0 } return s.sum() }

130 nil values and default values var t *tree dosum(t) // (*tree, nil) var i ints dosum(i) // (ints, nil) dosum(nil) // (nil, nil)

131 nil values and default values http.listenandserve("localhost:8080", nil)

132 use nil interfaces to signal default 零

133

134 nil is useful

135 nil is useful pointers methods can be called on nil receivers slices perfectly valid zero values maps perfect as read-only values channels essential for some concurrency patterns functions needed for completeness interfaces the most used signal in Go (err!= nil)

136 nil is an important part Go 零

137 let s not avoid nil

138 let s embrace nil golang.org/s/nil

Go Cheat Sheet. Operators. Go in a Nutshell. Declarations. Basic Syntax. Hello World. Functions. Comparison. Arithmetic. Credits

Go Cheat Sheet. Operators. Go in a Nutshell. Declarations. Basic Syntax. Hello World. Functions. Comparison. Arithmetic. Credits Credits Go Cheat Sheet Most example code taken from A Tour of Go, which is an excellent introduction to Go. If you're new to Go, do that tour. Seriously. Original HTML Cheat Sheet by Ariel Mashraki (a8m):

More information

GO IDIOMATIC CONVENTIONS EXPLAINED IN COLOR

GO IDIOMATIC CONVENTIONS EXPLAINED IN COLOR GO IDIOMATIC CONVENTIONS EXPLAINED IN COLOR REVISION 1 HAWTHORNE-PRESS.COM Go Idiomatic Conventions Explained in Color Published by Hawthorne-Press.com 916 Adele Street Houston, Texas 77009, USA 2013-2018

More information

Go Forth and Code. Jonathan Gertig. CSC 415: Programing Languages. Dr. Lyle

Go Forth and Code. Jonathan Gertig. CSC 415: Programing Languages. Dr. Lyle J o n a t h a n G e r t i g P a g e 1 Go Forth and Code Jonathan Gertig CSC 415: Programing Languages Dr. Lyle 2013 J o n a t h a n G e r t i g P a g e 2 Go dogs Go or A Brief History of Go 6 years ago

More information

go get my/vulnerabilities Green threads are not eco friendly threads

go get my/vulnerabilities Green threads are not eco friendly threads go get my/vulnerabilities Green threads are not eco friendly threads 1 Who ( Web Mobile ) penetration tester Code reviewer Programmer Roberto Clapis @empijei 2 Go Google s language Born in 2007 (quite

More information

Let s Go! Akim D le, Etienne Renault, Roland Levillain. June 8, TYLA Let s Go! June 8, / 58

Let s Go! Akim D le, Etienne Renault, Roland Levillain. June 8, TYLA Let s Go! June 8, / 58 Let s Go! Akim Demaille, Etienne Renault, Roland Levillain June 8, 2017 TYLA Let s Go! June 8, 2017 1 / 58 Table of contents 1 Overview 2 Language Syntax 3 Closure 4 Typed functional programming and Polymorphism

More information

COMP-520 GoLite Tutorial

COMP-520 GoLite Tutorial COMP-520 GoLite Tutorial Alexander Krolik Sable Lab McGill University Winter 2019 Plan Target languages Language constructs, emphasis on special cases General execution semantics Declarations Types Statements

More information

Go for Java Developers

Go for Java Developers Go for Java Developers Stoyan Rachev May 26-27 16, Sofia 1 Agenda Introduction Variables and Control Flow Types and Data Structures Functions Methods and Interfaces Concurrency Conclusion 2 What is Go?

More information

Lecture 22 Go http://xkcd.com/979/ Go developed ~2007 at Google by Robert Griesemer, Rob Pike, Ken Thompson open sourced in 2009 compiled, statically typed very fast compilation C-like syntax garbage collection

More information

Introduction to the Go Programming Language

Introduction to the Go Programming Language Introduction to the Go Programming Language Basics, Concurrency and Useful Packages Fabian Wenzelmann April 6, 2017 F. Wenzelmann Introduction to Go April 6, 2017 1 / 114 Why Go? What is Go? Go is a programming

More information

GO SHORT INTERVIEW QUESTIONS EXPLAINED IN COLOR

GO SHORT INTERVIEW QUESTIONS EXPLAINED IN COLOR GO SHORT INTERVIEW QUESTIONS EXPLAINED IN COLOR REVISION 1 HAWTHORNE-PRESS.COM Go Short Interview Questions Explained in Color Published by Hawthorne-Press.com 916 Adele Street Houston, Texas 77009, USA

More information

Pierce Ch. 3, 8, 11, 15. Type Systems

Pierce Ch. 3, 8, 11, 15. Type Systems Pierce Ch. 3, 8, 11, 15 Type Systems Goals Define the simple language of expressions A small subset of Lisp, with minor modifications Define the type system of this language Mathematical definition using

More information

CS201- Introduction to Programming Current Quizzes

CS201- Introduction to Programming Current Quizzes CS201- Introduction to Programming Current Quizzes Q.1 char name [] = Hello World ; In the above statement, a memory of characters will be allocated 13 11 12 (Ans) Q.2 A function is a block of statements

More information

Go Tutorial. To do. A brief, gentle intro to Go. Next Networking. q Today

Go Tutorial. To do. A brief, gentle intro to Go. Next Networking. q Today Go Tutorial To do q Today A brief, gentle intro to Go q Next Networking About Go Developed by Google Webpage: https://golang.org/ Concurrency was a priority in the language design A bit of a mix between

More information

The Go Programming Language. Frank Roberts

The Go Programming Language. Frank Roberts The Go Programming Language Frank Roberts frank.roberts@uky.edu - C++ (1983), Java (1995), Python (1991): not modern - Java is 18 years old; how has computing changed in 10? - multi/many core - web programming

More information

CS31 Discussion 1E Spring 17 : week 08

CS31 Discussion 1E Spring 17 : week 08 CS31 Discussion 1E Spring 17 : week 08 TA: Bo-Jhang Ho bojhang@cs.ucla.edu Credit to former TA Chelsea Ju Project 5 - Map cipher to crib Approach 1: For each pair of positions, check two letters in cipher

More information

C Review. MaxMSP Developers Workshop Summer 2009 CNMAT

C Review. MaxMSP Developers Workshop Summer 2009 CNMAT C Review MaxMSP Developers Workshop Summer 2009 CNMAT C Syntax Program control (loops, branches): Function calls Math: +, -, *, /, ++, -- Variables, types, structures, assignment Pointers and memory (***

More information

Distributed Systems. 02r. Go Programming. Paul Krzyzanowski. TA: Yuanzhen Gu. Rutgers University. Fall 2015

Distributed Systems. 02r. Go Programming. Paul Krzyzanowski. TA: Yuanzhen Gu. Rutgers University. Fall 2015 Distributed Systems 02r. Go Programming Paul Krzyzanowski TA: Yuanzhen Gu Rutgers University Fall 2015 September 15, 2015 CS 417 - Paul Krzyzanowski 1 Motivation In the current world, languages don't help

More information

developed ~2007 by Robert Griesemer, Rob Pike, Ken Thompson open source

developed ~2007 by Robert Griesemer, Rob Pike, Ken Thompson open source Go developed ~2007 by Robert Griesemer, Rob Pike, Ken Thompson open source compiled, statically typed syntax looks sort of like C garbage collection built-in concurrency no classes or type inheritance

More information

Introduzione a Go e RPC in Go

Introduzione a Go e RPC in Go Università degli Studi di Roma Tor Vergata Dipartimento di Ingegneria Civile e Ingegneria Informatica Introduzione a Go e RPC in Go Corso di Sistemi Distribuiti e Cloud Computing A.A. 2017/18 Valeria Cardellini

More information

Homework #3 CS2255 Fall 2012

Homework #3 CS2255 Fall 2012 Homework #3 CS2255 Fall 2012 MULTIPLE CHOICE 1. The, also known as the address operator, returns the memory address of a variable. a. asterisk ( * ) b. ampersand ( & ) c. percent sign (%) d. exclamation

More information

CS 61C: Great Ideas in Computer Architecture. C Arrays, Strings, More Pointers

CS 61C: Great Ideas in Computer Architecture. C Arrays, Strings, More Pointers CS 61C: Great Ideas in Computer Architecture C Arrays, Strings, More Pointers Instructor: Justin Hsia 6/20/2012 Summer 2012 Lecture #3 1 Review of Last Lecture C Basics Variables, Functions, Flow Control,

More information

Flow Control: Branches and loops

Flow Control: Branches and loops Flow Control: Branches and loops In this context flow control refers to controlling the flow of the execution of your program that is, which instructions will get carried out and in what order. In the

More information

Arrays Arrays and pointers Loops and performance Array comparison Strings. John Edgar 2

Arrays Arrays and pointers Loops and performance Array comparison Strings. John Edgar 2 CMPT 125 Arrays Arrays and pointers Loops and performance Array comparison Strings John Edgar 2 Python a sequence of data access elements with [index] index from [0] to [len-1] dynamic length heterogeneous

More information

Summary of Go Syntax /

Summary of Go Syntax / Summary of Go Syntax 02-201 / 02-601 Can declare 1 or more variables in same var statement Variables Can optionally provide initial values for all the variables (if omitted, each variable defaults to the

More information

William Kennedy. Brian Ketelsen Erik St. Martin Steve Francia FOREWORD BY MANNING WITH

William Kennedy. Brian Ketelsen Erik St. Martin Steve Francia FOREWORD BY MANNING WITH SAMPLE CHAPTER William Kennedy WITH FOREWORD BY Brian Ketelsen Erik St. Martin Steve Francia MANNING Go in Action by William Kennedy with Brian Ketelsen and Erik St. Martin Chapter 2 Copyright 2015 Manning

More information

CS61C Machine Structures. Lecture 4 C Pointers and Arrays. 1/25/2006 John Wawrzynek. www-inst.eecs.berkeley.edu/~cs61c/

CS61C Machine Structures. Lecture 4 C Pointers and Arrays. 1/25/2006 John Wawrzynek. www-inst.eecs.berkeley.edu/~cs61c/ CS61C Machine Structures Lecture 4 C Pointers and Arrays 1/25/2006 John Wawrzynek (www.cs.berkeley.edu/~johnw) www-inst.eecs.berkeley.edu/~cs61c/ CS 61C L04 C Pointers (1) Common C Error There is a difference

More information

CprE 288 Introduction to Embedded Systems Exam 1 Review. 1

CprE 288 Introduction to Embedded Systems Exam 1 Review.  1 CprE 288 Introduction to Embedded Systems Exam 1 Review http://class.ece.iastate.edu/cpre288 1 Overview of Today s Lecture Announcements Exam 1 Review http://class.ece.iastate.edu/cpre288 2 Announcements

More information

EMBEDDED SYSTEMS PROGRAMMING Language Basics

EMBEDDED SYSTEMS PROGRAMMING Language Basics EMBEDDED SYSTEMS PROGRAMMING 2015-16 Language Basics "The tower of Babel" by Pieter Bruegel the Elder Kunsthistorisches Museum, Vienna (PROGRAMMING) LANGUAGES ABOUT THE LANGUAGES C (1972) Designed to replace

More information

Lecture 14. No in-class files today. Homework 7 (due on Wednesday) and Project 3 (due in 10 days) posted. Questions?

Lecture 14. No in-class files today. Homework 7 (due on Wednesday) and Project 3 (due in 10 days) posted. Questions? Lecture 14 No in-class files today. Homework 7 (due on Wednesday) and Project 3 (due in 10 days) posted. Questions? Friday, February 11 CS 215 Fundamentals of Programming II - Lecture 14 1 Outline Static

More information

Dynamic Allocation in C

Dynamic Allocation in C Dynamic Allocation in C C Pointers and Arrays 1 The previous examples involved only targets that were declared as local variables. For serious development, we must also be able to create variables dynamically,

More information

C Pointers. 6th April 2017 Giulio Picierro

C Pointers. 6th April 2017 Giulio Picierro C Pointers 6th April 07 Giulio Picierro Functions Return type Function name Arguments list Function body int sum(int a, int b) { return a + b; } Return statement (return keyword

More information

CS2255 HOMEWORK #1 Fall 2012

CS2255 HOMEWORK #1 Fall 2012 CS55 HOMEWORK #1 Fall 01 1.What is assigned to the variable a given the statement below with the following assumptions: x = 10, y = 7, and z, a, and b are all int variables. a = x >= y; a. 10 b. 7 c. The

More information

CS 61c: Great Ideas in Computer Architecture

CS 61c: Great Ideas in Computer Architecture Arrays, Strings, and Some More Pointers June 24, 2014 Review of Last Lecture C Basics Variables, functioss, control flow, types, structs Only 0 and NULL evaluate to false Pointers hold addresses Address

More information

QUIZ. What is wrong with this code that uses default arguments?

QUIZ. What is wrong with this code that uses default arguments? QUIZ What is wrong with this code that uses default arguments? Solution The value of the default argument should be placed in either declaration or definition, not both! QUIZ What is wrong with this code

More information

APS105. Malloc and 2D Arrays. Textbook Chapters 6.4, Datatype Size

APS105. Malloc and 2D Arrays. Textbook Chapters 6.4, Datatype Size APS105 Malloc and 2D Arrays Textbook Chapters 6.4, 10.2 Datatype Size Datatypes have varying size: char: 1B int: 4B double: 8B int sizeof(): a builtin function that returns size of a type int x =

More information

Conditionals & Loops /

Conditionals & Loops / Conditionals & Loops 02-201 / 02-601 Conditionals If Statement if statements let you execute statements conditionally. true "then" part condition a > b false "else" part func max(a int, b int) int { var

More information

Pointers, Dynamic Data, and Reference Types

Pointers, Dynamic Data, and Reference Types Pointers, Dynamic Data, and Reference Types Review on Pointers Reference Variables Dynamic Memory Allocation The new operator The delete operator Dynamic Memory Allocation for Arrays 1 C++ Data Types simple

More information

Tokens, Expressions and Control Structures

Tokens, Expressions and Control Structures 3 Tokens, Expressions and Control Structures Tokens Keywords Identifiers Data types User-defined types Derived types Symbolic constants Declaration of variables Initialization Reference variables Type

More information

Issue with Implementing PrimeSieve() in Go

Issue with Implementing PrimeSieve() in Go Slices 02-201 Issue with Implementing PrimeSieve() in Go func PrimeSieve(n int) [n+1]bool { var iscomposite [n+1]bool //ERROR! biggestprime := 2 for biggestprime < n for i:=2; i

More information

CS2351 Data Structures. Lecture 7: A Brief Review of Pointers in C

CS2351 Data Structures. Lecture 7: A Brief Review of Pointers in C CS2351 Data Structures Lecture 7: A Brief Review of Pointers in C 1 About this lecture Pointer is a useful object that allows us to access different places in our memory We will review the basic use of

More information

Introduce C# as Object Oriented programming language. Explain, tokens,

Introduce C# as Object Oriented programming language. Explain, tokens, Module 2 98 Assignment 1 Introduce C# as Object Oriented programming language. Explain, tokens, lexicals and control flow constructs. 99 The C# Family Tree C Platform Independence C++ Object Orientation

More information

The Awesomeness of Go. Igor Lankin DevFest Karlsruhe, Nov 2016

The Awesomeness of Go. Igor Lankin DevFest Karlsruhe, Nov 2016 The Awesomeness of Go Igor Lankin DevFest Karlsruhe, Nov 2016 Igor Lankin Software Developer @ inovex C#, Java, Java Script, full-time GO (waipu.tv ) 2 What is Go? 3 An Awesome Programming Language 4 Imagine

More information

P.G.TRB - COMPUTER SCIENCE. c) data processing language d) none of the above

P.G.TRB - COMPUTER SCIENCE. c) data processing language d) none of the above P.G.TRB - COMPUTER SCIENCE Total Marks : 50 Time : 30 Minutes 1. C was primarily developed as a a)systems programming language b) general purpose language c) data processing language d) none of the above

More information

Flow Control. CSC215 Lecture

Flow Control. CSC215 Lecture Flow Control CSC215 Lecture Outline Blocks and compound statements Conditional statements if - statement if-else - statement switch - statement? : opertator Nested conditional statements Repetitive statements

More information

Cut. it s not just for Google. Eleanor McHugh.

Cut. it s not just for Google. Eleanor McHugh. Ro u gh Cut! Go it s not just for Google Eleanor McHugh http://slides.games-with-brains.net/ compiled garbage collected imperative package main import fmt const HELLO string = hello var WORLD string =

More information

Don t Go Java! Edition 2019

Don t Go Java! Edition 2019 Don t Go, Java! Don t Go Java! Don t Go Java! Edition 2019 Disclaimer Disclaimer I actually like Go! Guess The Movie Guess The Movie Guess The Movie Guess The Movie Who s That Dude? Chris Engelbert Senior

More information

COMP 202 Java in one week

COMP 202 Java in one week COMP 202 Java in one week... Continued CONTENTS: Return to material from previous lecture At-home programming exercises Please Do Ask Questions It's perfectly normal not to understand everything Most of

More information

EMBEDDED SYSTEMS PROGRAMMING Language Basics

EMBEDDED SYSTEMS PROGRAMMING Language Basics EMBEDDED SYSTEMS PROGRAMMING 2014-15 Language Basics (PROGRAMMING) LANGUAGES "The tower of Babel" by Pieter Bruegel the Elder Kunsthistorisches Museum, Vienna ABOUT THE LANGUAGES C (1972) Designed to replace

More information

Discussion 1E. Jie(Jay) Wang Week 10 Dec.2

Discussion 1E. Jie(Jay) Wang Week 10 Dec.2 Discussion 1E Jie(Jay) Wang Week 10 Dec.2 Outline Dynamic memory allocation Class Final Review Dynamic Allocation of Memory Recall int len = 100; double arr[len]; // error! What if I need to compute the

More information

Structure and Interpretation of Computer Programs

Structure and Interpretation of Computer Programs CS 6A Spring 203 Structure and Interpretation of Computer Programs Final Solutions INSTRUCTIONS You have 3 hours to complete the exam. The exam is closed book, closed notes, closed computer, closed calculator,

More information

Intro. Scheme Basics. scm> 5 5. scm>

Intro. Scheme Basics. scm> 5 5. scm> Intro Let s take some time to talk about LISP. It stands for LISt Processing a way of coding using only lists! It sounds pretty radical, and it is. There are lots of cool things to know about LISP; if

More information

Reference slides! C Strings! A string in C is just an array of characters.!!!char string[] = "abc";! How do you tell how long a string is?!

Reference slides! C Strings! A string in C is just an array of characters.!!!char string[] = abc;! How do you tell how long a string is?! CS61C L04 Introduction to C (pt 2) (1)! Reference slides! C Strings! You ARE responsible for the material on these slides (they re just taken from the reading anyway). These were the slides that generated

More information

Operating Systems CMPSCI 377, Lec 2 Intro to C/C++ Prashant Shenoy University of Massachusetts Amherst

Operating Systems CMPSCI 377, Lec 2 Intro to C/C++ Prashant Shenoy University of Massachusetts Amherst Operating Systems CMPSCI 377, Lec 2 Intro to C/C++ Prashant Shenoy University of Massachusetts Amherst Department of Computer Science Why C? Low-level Direct access to memory WYSIWYG (more or less) Effectively

More information

C++ ARRAYS POINTERS POINTER ARITHMETIC. Problem Solving with Computers-I

C++ ARRAYS POINTERS POINTER ARITHMETIC. Problem Solving with Computers-I C++ ARRAYS POINTERS POINTER ARITHMETIC Problem Solving with Computers-I General model of memory Sequence of adjacent cells Each cell has 1-byte stored in it Each cell has an address (memory location) Memory

More information

Creating a C++ Program

Creating a C++ Program Program A computer program (also software, or just a program) is a sequence of instructions written in a sequence to perform a specified task with a computer. 1 Creating a C++ Program created using an

More information

Go Tutorial. Arjun Roy CSE 223B, Spring 2017

Go Tutorial. Arjun Roy CSE 223B, Spring 2017 Go Tutorial Arjun Roy arroy@eng.ucsd.edu CSE 223B, Spring 2017 Administrative details TA Office Hours: EBU3B B250A, Tuesday 5-7PM TA Email: arroy@eng.ucsd.edu All labs due by 2359 PDT. Lab 1 due: 4/13/2017.

More information

In this assignment, you will implement a basic CHORD distributed hash table (DHT) as described in this paper:

In this assignment, you will implement a basic CHORD distributed hash table (DHT) as described in this paper: Project 2: Chord Distributed Hash Table Introduction In this assignment, you will implement a basic CHORD distributed hash table (DHT) as described in this paper: https://pdos.csail.mit.edu/papers/ton:chord/paper-ton.pdf

More information

Go Concurrent Programming. QCon2018 Beijing

Go Concurrent Programming. QCon2018 Beijing Go Concurrent Programming chao.cai@mobvista.com QCon2018 Beijing Shared Memory Model Shared Memory Model class Worker implements Runnable{ private volatile boolean isrunning = false; @Override public void

More information

PHPoC vs PHP > Overview. Overview

PHPoC vs PHP > Overview. Overview PHPoC vs PHP > Overview Overview PHPoC is a programming language that Sollae Systems has developed. All of our PHPoC products have PHPoC interpreter in firmware. PHPoC is based on a wide use script language

More information

FORM 1 (Please put your name and section number (001/10am or 002/2pm) on the scantron!!!!) CS 161 Exam II: True (A)/False(B) (2 pts each):

FORM 1 (Please put your name and section number (001/10am or 002/2pm) on the scantron!!!!) CS 161 Exam II: True (A)/False(B) (2 pts each): FORM 1 (Please put your name and section number (001/10am or 002/2pm) on the scantron!!!!) CS 161 Exam II: True (A)/False(B) (2 pts each): 1. If a function has default arguments, they can be located anywhere

More information

Jagannath Institute of Management Sciences Lajpat Nagar. BCA II Sem. C Programming

Jagannath Institute of Management Sciences Lajpat Nagar. BCA II Sem. C Programming Jagannath Institute of Management Sciences Lajpat Nagar BCA II Sem C Programming UNIT I Pointers: Introduction to Pointers, Pointer Notation,Decalaration and Initialization, Accessing variable through

More information

Control Structures. Important Semantic Difference

Control Structures. Important Semantic Difference Control Structures Important Semantic Difference In all of these loops we are going to discuss, the braces are ALWAYS REQUIRED. Even if your loop/block only has one statement, you must include the braces.

More information

Dynamic Allocation in C

Dynamic Allocation in C Dynamic Allocation in C 1 The previous examples involved only targets that were declared as local variables. For serious development, we must also be able to create variables dynamically, as the program

More information

Reference slides! Garcia, Fall 2011 UCB! CS61C L04 Introduction to C (pt 2) (1)!

Reference slides! Garcia, Fall 2011 UCB! CS61C L04 Introduction to C (pt 2) (1)! Reference slides! You ARE responsible for the material on these slides (they re just taken from the reading anyway). These were the slides that generated the fewest questions in years past (i.e., those

More information

Lecture Notes on Queues

Lecture Notes on Queues Lecture Notes on Queues 15-122: Principles of Imperative Computation Frank Pfenning Lecture 9 September 25, 2012 1 Introduction In this lecture we introduce queues as a data structure and linked lists

More information

Basic Types, Variables, Literals, Constants

Basic Types, Variables, Literals, Constants Basic Types, Variables, Literals, Constants What is in a Word? A byte is the basic addressable unit of memory in RAM Typically it is 8 bits (octet) But some machines had 7, or 9, or... A word is the basic

More information

PHPoC. PHPoC vs PHP. Version 1.1. Sollae Systems Co., Ttd. PHPoC Forum: Homepage:

PHPoC. PHPoC vs PHP. Version 1.1. Sollae Systems Co., Ttd. PHPoC Forum:  Homepage: PHPoC PHPoC vs PHP Version 1.1 Sollae Systems Co., Ttd. PHPoC Forum: http://www.phpoc.com Homepage: http://www.eztcp.com Contents 1 Overview...- 3 - Overview...- 3-2 Features of PHPoC (Differences from

More information

Lecture 9: Lists. Lists store lists of variables. Declaring variables that hold lists. Carl Kingsford, , Fall 2015

Lecture 9: Lists. Lists store lists of variables. Declaring variables that hold lists. Carl Kingsford, , Fall 2015 Carl Kingsford, 0-0, Fall 0 Lecture : Lists Terminology: Go uses a non-standard term slice to refer to what we are calling lists. Others use the term array for the same concept. Unfortunately, Go uses

More information

M1-R4: Programing and Problem Solving using C (JAN 2019)

M1-R4: Programing and Problem Solving using C (JAN 2019) M1-R4: Programing and Problem Solving using C (JAN 2019) Max Marks: 100 M1-R4-07-18 DURATION: 03 Hrs 1. Each question below gives a multiple choice of answers. Choose the most appropriate one and enter

More information

Short Notes of CS201

Short Notes of CS201 #includes: Short Notes of CS201 The #include directive instructs the preprocessor to read and include a file into a source code file. The file name is typically enclosed with < and > if the file is a system

More information

Introduction to C Language (M3-R )

Introduction to C Language (M3-R ) Introduction to C Language (M3-R4-01-18) 1. Each question below gives a multiple choice of answers. Choose the most appropriate one and enter in OMR answer sheet supplied with the question paper, following

More information

BBM 201 DATA STRUCTURES

BBM 201 DATA STRUCTURES BBM 201 DATA STRUCTURES Lecture 8: Dynamically Allocated Linked Lists 2017-2018 Fall int x; x = 8; int A[4]; An array is stored as one contiguous block of memory. How can we add a fifth element to the

More information

GO - QUICK GUIDE GO - OVERVIEW

GO - QUICK GUIDE GO - OVERVIEW http://www.tutorialspoint.com/go/go_quick_guide.htm GO - QUICK GUIDE Copyright tutorialspoint.com GO - OVERVIEW Go is a general-purpose language designed with systems programming in mind.it was initially

More information

QUIZ. What are 3 differences between C and C++ const variables?

QUIZ. What are 3 differences between C and C++ const variables? QUIZ What are 3 differences between C and C++ const variables? Solution QUIZ Source: http://stackoverflow.com/questions/17349387/scope-of-macros-in-c Solution The C/C++ preprocessor substitutes mechanically,

More information

CS201 - Introduction to Programming Glossary By

CS201 - Introduction to Programming Glossary By CS201 - Introduction to Programming Glossary By #include : The #include directive instructs the preprocessor to read and include a file into a source code file. The file name is typically enclosed with

More information

Software Engineering using Formal Methods

Software Engineering using Formal Methods Software Engineering using Formal Methods Introduction to Promela Wolfgang Ahrendt 03 September 2015 SEFM: Promela /GU 150903 1 / 36 Towards Model Checking System Model Promela Program byte n = 0; active

More information

FOR Loop. FOR Loop has three parts:initialization,condition,increment. Syntax. for(initialization;condition;increment){ body;

FOR Loop. FOR Loop has three parts:initialization,condition,increment. Syntax. for(initialization;condition;increment){ body; CLASSROOM SESSION Loops in C Loops are used to repeat the execution of statement or blocks There are two types of loops 1.Entry Controlled For and While 2. Exit Controlled Do while FOR Loop FOR Loop has

More information

A Fast Review of C Essentials Part I

A Fast Review of C Essentials Part I A Fast Review of C Essentials Part I Structural Programming by Z. Cihan TAYSI Outline Program development C Essentials Functions Variables & constants Names Formatting Comments Preprocessor Data types

More information

Lecture 2: C Programm

Lecture 2: C Programm 0 3 E CS 1 Lecture 2: C Programm ing C Programming Procedural thought process No built in object abstractions data separate from methods/functions Low memory overhead compared to Java No overhead of classes

More information

WHAT POINTERS REALLY ARE

WHAT POINTERS REALLY ARE POINTERS What is a pointer? The index of a book contains pointers. A URL (e.g., http://turing.ubishops.ca/home/cs318) is a pointer. A street address is a pointer. What is then a forwarding address? a pointer

More information

The issues. Programming in C++ Common storage modes. Static storage in C++ Session 8 Memory Management

The issues. Programming in C++ Common storage modes. Static storage in C++ Session 8 Memory Management Session 8 Memory Management The issues Dr Christos Kloukinas City, UoL http://staff.city.ac.uk/c.kloukinas/cpp (slides originally produced by Dr Ross Paterson) Programs manipulate data, which must be stored

More information

FORM 2 (Please put your name and form # on the scantron!!!!)

FORM 2 (Please put your name and form # on the scantron!!!!) CS 161 Exam 2: FORM 2 (Please put your name and form # on the scantron!!!!) True (A)/False(B) (2 pts each): 1. Recursive algorithms tend to be less efficient than iterative algorithms. 2. A recursive function

More information

Agenda. Peer Instruction Question 1. Peer Instruction Answer 1. Peer Instruction Question 2 6/22/2011

Agenda. Peer Instruction Question 1. Peer Instruction Answer 1. Peer Instruction Question 2 6/22/2011 CS 61C: Great Ideas in Computer Architecture (Machine Structures) Introduction to C (Part II) Instructors: Randy H. Katz David A. Patterson http://inst.eecs.berkeley.edu/~cs61c/sp11 Spring 2011 -- Lecture

More information

Pointers. A pointer is simply a reference to a variable/object. Compilers automatically generate code to store/retrieve variables from memory

Pointers. A pointer is simply a reference to a variable/object. Compilers automatically generate code to store/retrieve variables from memory Pointers A pointer is simply a reference to a variable/object Compilers automatically generate code to store/retrieve variables from memory It is automatically generating internal pointers We don t have

More information

CS61C : Machine Structures

CS61C : Machine Structures inst.eecs.berkeley.edu/~cs61c CS61C : Machine Structures Lecture #3 C Strings, Arrays, & Malloc 2007-06-27 Scott Beamer, Instructor Sun announces new supercomputer: Sun Constellation CS61C L3 C Pointers

More information

Lecture 10 Notes Linked Lists

Lecture 10 Notes Linked Lists Lecture 10 Notes Linked Lists 15-122: Principles of Imperative Computation (Summer 1 2015) Frank Pfenning, Rob Simmons, André Platzer 1 Introduction In this lecture we discuss the use of linked lists to

More information

Vector and Free Store (Pointers and Memory Allocation)

Vector and Free Store (Pointers and Memory Allocation) DM560 Introduction to Programming in C++ Vector and Free Store (Pointers and Memory Allocation) Marco Chiarandini Department of Mathematics & Computer Science University of Southern Denmark [Based on slides

More information

Heap Arrays and Linked Lists. Steven R. Bagley

Heap Arrays and Linked Lists. Steven R. Bagley Heap Arrays and Linked Lists Steven R. Bagley Recap Data is stored in variables Can be accessed by the variable name Or in an array, accessed by name and index Variables and arrays have a type Create our

More information

Introduction to C: Pointers

Introduction to C: Pointers Introduction to C: Pointers Nils Moschüring PhD Student (LMU) Nils Moschüring PhD Student (LMU), Introduction to C: Pointers 1 1 Introduction 2 Pointers Basics Useful: Function

More information

A brief introduction to C programming for Java programmers

A brief introduction to C programming for Java programmers A brief introduction to C programming for Java programmers Sven Gestegård Robertz September 2017 There are many similarities between Java and C. The syntax in Java is basically

More information

Variables Data types Variable I/O. C introduction. Variables. Variables 1 / 14

Variables Data types Variable I/O. C introduction. Variables. Variables 1 / 14 C introduction Variables Variables 1 / 14 Contents Variables Data types Variable I/O Variables 2 / 14 Usage Declaration: t y p e i d e n t i f i e r ; Assignment: i d e n t i f i e r = v a l u e ; Definition

More information

Kurt Schmidt. October 30, 2018

Kurt Schmidt. October 30, 2018 to Structs Dept. of Computer Science, Drexel University October 30, 2018 Array Objectives to Structs Intended audience: Student who has working knowledge of Python To gain some experience with a statically-typed

More information

Tranquility Publications. Web Edition MAC

Tranquility Publications. Web Edition MAC Web Edition 2019 -MAC 2 Go Go language is a programming language initially developed at Google in the year 2007 by Robert Griesemer, Rob Pike, and Ken Thompson. It is a statically-typed language having

More information

520 Principles of Programming Languages. Arithmetic. Variable Declarations. 19: Pascal

520 Principles of Programming Languages. Arithmetic. Variable Declarations. 19: Pascal Structure of a Pascal Program 520 Principles of Programming Languages 19: Pascal Christian Collberg collberg@cs.arizona.edu Department of Computer Science University of Arizona PROGRAM Name (list of files);

More information

Formal Specification and Verification

Formal Specification and Verification Formal Specification and Verification Introduction to Promela Bernhard Beckert Based on a lecture by Wolfgang Ahrendt and Reiner Hähnle at Chalmers University, Göteborg Formal Specification and Verification:

More information

Spin: Overview of PROMELA

Spin: Overview of PROMELA Spin: Overview of PROMELA Patrick Trentin patrick.trentin@unitn.it http://disi.unitn.it/trentin Formal Methods Lab Class, March 10, 2017 These slides are derived from those by Stefano Tonetta, Alberto

More information

COMPUTER APPLICATION

COMPUTER APPLICATION Total No. of Printed Pages 16 HS/XII/A.Sc.Com/CAP/14 2 0 1 4 COMPUTER APPLICATION ( Science / Arts / Commerce ) ( Theory ) Full Marks : 70 Time : 3 hours The figures in the margin indicate full marks for

More information

COMP520 - GoLite Type Checking Specification

COMP520 - GoLite Type Checking Specification COMP520 - GoLite Type Checking Specification Vincent Foley February 26, 2015 1 Declarations Declarations are the primary means of introducing new identifiers in the symbol table. In Go, top-level declarations

More information

2.1. Chapter 2: Parts of a C++ Program. Parts of a C++ Program. Introduction to C++ Parts of a C++ Program

2.1. Chapter 2: Parts of a C++ Program. Parts of a C++ Program. Introduction to C++ Parts of a C++ Program Chapter 2: Introduction to C++ 2.1 Parts of a C++ Program Copyright 2009 Pearson Education, Inc. Publishing as Pearson Addison-Wesley 2-1 Parts of a C++ Program Parts of a C++ Program // sample C++ program

More information