DOCSLIB.ORG

Exam 1 Review: Solutions Capture the Dragons

Total Page：16

File Type：pdf, Size：1020Kb

Download full-text PDF Read full-text
Exam 1 Review: Solutions Capture the Dragons CSCI 1101B: Introduction to Computer Science Instructor: Prof. Harmon Exam 1 Review: Solutions Capture the Dragons Boolean Expressions 1. Of the following, which are Boolean expressions? (a)2+3 Not Boolean (b)2>3 Boolean (c) num >= 2 Boolean (d) num1 = num2 Not Boolean 2. If x = 3, and x <= y evaluates to True, what values can y have? y >= 3 3. Simplify each of the following expressions: (a) my_num or True Depends on what the value of my_num is. See rules as in #5. (b) False and "Mary" or True True (c) False and ("Mary" or True) False 4. Is x =< y the same as x <= y? No. Python only recognizes the latter. The former is invalid syntax. 5. If x = 1 and y = 2, explain the following results: (a) >>> x and y # = 2 (b) >>> x or y # = 1 Python uses lazy evaluation. • The expression x and y first evaluates x. If x is equivalent to False (or empty/zero), its value is returned. Otherwise, y is evaluated and the resulting value is returned. • The expression x or y first evaluates x. If x is equivalent to True (or non-empty/nonzero), its value is returned. Otherwise, y is evaluated and the resulting value is returned. 1 CSCI 1101B: Introduction to Computer Science Exam 1 Review: Solutions Conditionals 1. What is indentation, and how is it related to the concept of a code block? Indentation is the placement of text (to the left or right). Python uses indenta- tion to associate code into groups, or blocks. 2. What is the difference between a chained conditional and a nested conditional? Chained => if, elif, else Nested => conditionals exist (are "nested") inside each other 3. Simplify the following: x = -67 if x < 0: print("Negative, lieutenant.") else: ifx>0: print("I'm positive.") else: print("My hero, zero!") This code becomes more readable by changing the nested conditional into a chained conditional. 4. What will the following code print given that x = 3, y = 5, and z = 2? ifx<y and x < z: print("even if you're little") elify<x and y < z: print("you can doa lot") else: print("no matter what they tell you") The "no matter what they tell you" case will be printed. Functions 1. What is a function signature, and why is it useful? The function signature tells us the data type for the inputs and outputs of our function. 2. What is the difference between... (a) ...an argument and a parameter? An argument is an actual value passed into the function. A parameter is the variable that is named in the function header. (b) ...a function and a procedure? Both are functions, but a procedure does not return any value. 3. What does scope mean in programming? Can you give an example? Examples vary. Broadly, the scope of some entity refers to which parts of a program and see and/or use that entity. 4. What is the control flow (flow of execution) for the following program: def times_42(num): return num * 42 times_42() Python reads the function header, and then the function call. Because no argu- ment is provided, there will be an error. 2 CSCI 1101B: Introduction to Computer Science Exam 1 Review: Solutions Methods 1. What’s the difference between a built-in function, a method, and a module? A module is a file (can have variables and functions inside). A method is a kind of function that is associated with a class of object. A built-in function performs a common operation and can be used for multiple types. 2. What does "Go U Bears!".isupper() evaluate to? False 3. Can you simplify the above expression to "Go U Bears!".upper()? No 4. Your friend tells you that the following code keeps resulting in a ValueError: daisy_idx = my_string.index("daisies") What advice would you give them? Use find() instead. 5. What does the following evaluate to? ("dance"*2+"rev").rfind("dance") 5 Strings 1. What’s the difference between "\n" and "\t"? Newline vs. tab 2. Given two strings a and b, write an expression that will evaluate to the difference between the length of a and the length of b. For example, if a = "pizza" (length 5) and b = "cat" (length 3), your expression should yield 2. abs(len(a) - len(b)) 3. Given an arbitrary string named s, how would you use slicing notation to retrieve: (a) The first letter? s[0] or s[0:1] (b) The last letter? s[-1] or s[-1:] (c) The first two characters? s[0:2] or s[:2] (d) The substring starting from index 4 until the end of the string? s[4:] 3 CSCI 1101B: Introduction to Computer Science Exam 1 Review: Solutions Types 1. What is the difference between 3 and "3"? 3 is an int value. "3" is a string value. 2. How do we check the type of a data value? With the built-in type() function. 3. What is the function signature for abs()? (number or bool) ! number 4. List the operators we have talked about in order of precedence (Hint: there are at least 27 across the following categories: arithmetic, comparison, equality, assignment, membership, and logical). Operator Category () Arithmetic ** Arithmetic +, - (unary) Arithmetic *, /, //, % Arithmetic +, - (binary) Arithmetic <, <=, >, >= Comparison ==, != Equality =, +=, -=, /=, *=, **=, %=, //= Assignment in Membership and, or, not Logical 5. What types of operands (int, float, string, or bool) are acceptable for each of the arith- metic operators +, -, *, and /? Is the output the same regardless of the data type of the operands? No, the output will not be the same. You can experiment in the shell to see what happens in each case. 4.
Load more

Recommended publications
  • CSCI 2041: Lazy Evaluation
    CSCI 2041: Lazy Evaluation Chris Kauffman Last Updated: Wed Dec 5 12:32:32 CST 2018 1 Logistics Reading Lab13: Lazy/Streams I Module Lazy on lazy Covers basics of delayed evaluation computation I Module Stream on streams A5: Calculon Lambdas/Closures I Arithmetic language Briefly discuss these as they interpreter pertain Calculon I 2X credit for assignment I 5 Required Problems 100pts Goals I 5 Option Problems 50pts I Eager Evaluation I Milestone due Wed 12/5 I Lazy Evaluation I Final submit Tue 12/11 I Streams 2 Evaluation Strategies Eager Evaluation Lazy Evaluation I Most languages employ I An alternative is lazy eager evaluation evaluation I Execute instructions as I Execute instructions only as control reaches associated expression results are needed code (call by need) I Corresponds closely to I Higher-level idea with actual machine execution advantages and disadvantages I In pure computations, evaluation strategy doesn’t matter: will produce the same results I With side-effects, when code is run matter, particular for I/O which may see different printing orders 3 Exercise: Side-Effects and Evaluation Strategy Most common place to see differences between Eager/Lazy eval is when functions are called I Eager eval: eval argument expressions, call functions with results I Lazy eval: call function with un-evaluated expressions, eval as results are needed Consider the following expression let print_it expr = printf "Printing it\n"; printf "%d\n" expr; ;; print_it (begin printf "Evaluating\n"; 5; end);; Predict results and output for both Eager and Lazy Eval strategies 4 Answers: Side-Effects and Evaluation Strategy let print_it expr = printf "Printing it\n"; printf "%d\n" expr; ;; print_it (begin printf "Evaluating\n"; 5; end);; Evaluation > ocamlc eager_v_lazy.ml > ./a.out Eager Eval # ocaml’s default Evaluating Printing it 5 Lazy Eval Printing it Evaluating 5 5 OCaml and explicit lazy Computations I OCaml’s default model is eager evaluation BUT.
    [Show full text]
  • Control Flow
    Control Flow COMS W4115 Prof. Stephen A. Edwards Spring 2002 Columbia University Department of Computer Science Control Flow “Time is Nature’s way of preventing everything from happening at once.” Scott identifies seven manifestations of this: 1. Sequencing foo(); bar(); 2. Selection if (a) foo(); 3. Iteration while (i<10) foo(i); 4. Procedures foo(10,20); 5. Recursion foo(int i) { foo(i-1); } 6. Concurrency foo() jj bar() 7. Nondeterminism do a -> foo(); [] b -> bar(); Ordering Within Expressions What code does a compiler generate for a = b + c + d; Most likely something like tmp = b + c; a = tmp + d; (Assumes left-to-right evaluation of expressions.) Order of Evaluation Why would you care? Expression evaluation can have side-effects. Floating-point numbers don’t behave like numbers. Side-effects int x = 0; int foo() { x += 5; return x; } int a = foo() + x + foo(); What’s the final value of a? Side-effects int x = 0; int foo() { x += 5; return x; } int a = foo() + x + foo(); GCC sets a=25. Sun’s C compiler gave a=20. C says expression evaluation order is implementation-dependent. Side-effects Java prescribes left-to-right evaluation. class Foo { static int x; static int foo() { x += 5; return x; } public static void main(String args[]) { int a = foo() + x + foo(); System.out.println(a); } } Always prints 20. Number Behavior Basic number axioms: a + x = a if and only if x = 0 Additive identity (a + b) + c = a + (b + c) Associative a(b + c) = ab + ac Distributive Misbehaving Floating-Point Numbers 1e20 + 1e-20 = 1e20 1e-20 1e20 (1 + 9e-7) + 9e-7 6= 1 + (9e-7 + 9e-7) 9e-7 1, so it is discarded, however, 1.8e-6 is large enough 1:00001(1:000001 − 1) 6= 1:00001 · 1:000001 − 1:00001 · 1 1:00001 · 1:000001 = 1:00001100001 requires too much intermediate precision.
    [Show full text]
  • 210 CHAPTER 7. NAMES and BINDING Chapter 8
    210 CHAPTER 7. NAMES AND BINDING Chapter 8 Expressions and Evaluation Overview This chapter introduces the concept of the programming environment and the role of expressions in a program. Programs are executed in an environment which is provided by the operating system or the translator. An editor, linker, file system, and compiler form the environment in which the programmer can enter and run programs. Interac- tive language systems, such as APL, FORTH, Prolog, and Smalltalk among others, are embedded in subsystems which replace the operating system in forming the program- development environment. The top-level control structure for these subsystems is the Read-Evaluate-Write cycle. The order of computation within a program is controlled in one of three basic ways: nesting, sequencing, or signaling other processes through the shared environment or streams which are managed by the operating system. Within a program, an expression is a nest of function calls or operators that returns a value. Binary operators written between their arguments are used in infix syntax. Unary and binary operators written before a single argument or a pair of arguments are used in prefix syntax. In postfix syntax, operators (unary or binary) follow their arguments. Parse trees can be developed from expressions that include infix, prefix and postfix operators. Rules for precedence, associativity, and parenthesization determine which operands belong to which operators. The rules that define order of evaluation for elements of a function call are as follows: • Inside-out: Evaluate every argument before beginning to evaluate the function. 211 212 CHAPTER 8. EXPRESSIONS AND EVALUATION • Outside-in: Start evaluating the function body.
    [Show full text]
  • Top Functional Programming Languages Based on Sentiment Analysis 2021 11
    POWERED BY: TOP FUNCTIONAL PROGRAMMING LANGUAGES BASED ON SENTIMENT ANALYSIS 2021 Functional Programming helps companies build software that is scalable, and less prone to bugs, which means that software is more reliable and future-proof. It gives developers the opportunity to write code that is clean, elegant, and powerful. Functional Programming is used in demanding industries like eCommerce or streaming services in companies such as Zalando, Netflix, or Airbnb. Developers that work with Functional Programming languages are among the highest paid in the business. I personally fell in love with Functional Programming in Scala, and that’s why Scalac was born. I wanted to encourage both companies, and developers to expect more from their applications, and Scala was the perfect answer, especially for Big Data, Blockchain, and FinTech solutions. I’m glad that my marketing and tech team picked this topic, to prepare the report that is focused on sentiment - because that is what really drives people. All of us want to build effective applications that will help businesses succeed - but still... We want to have some fun along the way, and I believe that the Functional Programming paradigm gives developers exactly that - fun, and a chance to clearly express themselves solving complex challenges in an elegant code. LUKASZ KUCZERA, CEO AT SCALAC 01 Table of contents Introduction 03 What Is Functional Programming? 04 Big Data and the WHY behind the idea of functional programming. 04 Functional Programming Languages Ranking 05 Methodology 06 Brand24
    [Show full text]
  • CS1101S Studio Session Week 11: Stream
    Welcome CS1101S Studio Session Week 11: Stream Niu Yunpeng [email protected] October 30, 2018 Niu Yunpeng CS1101S Studio Week 11 October 30, 2018 1 / 27 Overview 1 Lazy evaluation Computational model Function application 2 Stream Delayed evaluation Stream programming Niu Yunpeng CS1101S Studio Week 11 October 30, 2018 2 / 27 Lazy Evaluation Computational model Computational model is a useful guideline for us to understand how the interpreter works. Computational model may vary depending on programming language and the runtime system used. In CS1101S, we introduce two computational models: substitution model and environment model. What to expect In the coming weeks, these two models will still be valid. Niu Yunpeng CS1101S Studio Week 11 October 30, 2018 3 / 27 Lazy Evaluation Substitution model For stateless programming only: Evaluate all actual arguments; Replace all formal parameters with their actual arguments; Apply each statement in the function body (and get the return value); Repeat the first 3 steps until done. Niu Yunpeng CS1101S Studio Week 11 October 30, 2018 4 / 27 Lazy Evaluation Environment model For stateful programming: Each frame contains a series of bindings of names and values. The value of a variable depends on its environment, a sequence of frames up to the global frame. Each function call will create a new frame and extend its enclosing environment. Niu Yunpeng CS1101S Studio Week 11 October 30, 2018 5 / 27 Lazy Evaluation Function in JavaScript Function in JavaScript is a first-class citizen (object). They have a call method. The call method is triggered when this function is applied. Function application When a function is applied, “this” is prepanded to the list of parameters.
    [Show full text]
  • Monads for Functional Programming
    Monads for functional programming Philip Wadler, University of Glasgow? Department of Computing Science, University of Glasgow, G12 8QQ, Scotland ([email protected]) Abstract. The use of monads to structure functional programs is de- scribed. Monads provide a convenient framework for simulating effects found in other languages, such as global state, exception handling, out- put, or non-determinism. Three case studies are looked at in detail: how monads ease the modification of a simple evaluator; how monads act as the basis of a datatype of arrays subject to in-place update; and how monads can be used to build parsers. 1 Introduction Shall I be pure or impure? The functional programming community divides into two camps. Pure lan- guages, such as Miranda0 and Haskell, are lambda calculus pure and simple. Impure languages, such as Scheme and Standard ML, augment lambda calculus with a number of possible effects, such as assignment, exceptions, or continu- ations. Pure languages are easier to reason about and may benefit from lazy evaluation, while impure languages offer efficiency benefits and sometimes make possible a more compact mode of expression. Recent advances in theoretical computing science, notably in the areas of type theory and category theory, have suggested new approaches that may integrate the benefits of the pure and impure schools. These notes describe one, the use of monads to integrate impure effects into pure functional languages. The concept of a monad, which arises from category theory, has been applied by Moggi to structure the denotational semantics of programming languages [13, 14]. The same technique can be applied to structure functional programs [21, 23].
    [Show full text]
  • The Scala Programming Language
    The Scala Programming Language Mooly Sagiv Slides taken from Martin Odersky (EPFL) Donna Malayeri (CMU) Hila Peleg (TAU) Modern Functional Programming • Higher order • Modules • Pattern matching • Statically typed with type inference • Two viable alternatives • Haskel • Pure lazy evaluation and higher order programming leads to Concise programming • Support for domain specific languages • I/O Monads • Type classes • OCaml • Encapsulated side-effects via references Then Why aren’t FP adapted? • Education • Lack of OO support • Subtyping increases the complexity of type inference • Programmers seeks control on the exact implementation • Imperative programming is natural in certain situations Why Scala? (Coming from OCaml) • Runs on the JVM/.NET • Can use any Java code in Scala • Combines functional and imperative programming in a smooth way • Effective library • Inheritance • General modularity mechanisms The Java Programming Language • Designed by Sun 1991-95 • Statically typed and type safe • Clean and Powerful libraries • Clean references and arrays • Object Oriented with single inheritance • Interfaces with multiple inhertitence • Portable with JVM • Effective JIT compilers • Support for concurrency • Useful for Internet Java Critique • Downcasting reduces the effectiveness of static type checking • Many of the interesting errors caught at runtime • Still better than C, C++ • Huge code blowouts • Hard to define domain specific knowledge • A lot of boilerplate code • Sometimes OO stands in our way • Generics only partially helps Why
    [Show full text]
  • Comparison Between Lazy and Strict Evaluation
    View metadata, citation and similar papers at core.ac.uk brought to you by CORE provided by Trepo - Institutional Repository of Tampere University Nayeong Song Comparison between lazy and strict evaluation Bachelor’s thesis Faculty of Information Technology and Communication Sciences (ITC) Examiner: Maarit Harsu Oct 2020 i ABSTRACT Nayeong Song: Comparison between lazy and strict evaluation Bachelor’s thesis Tampere University Bachelor’s Degree Programme in Science and Engineering Oct 2020 Evaluation strategy is the way to defne the order of function call’s argument’s evaluation. Most of the today’s programming languages employ strict programming paradigm, which is focused mostly on call-by-value and call-by-reference. However, call-by-name or call-by-need, which evaluates the expression lazily, is used only in functional programming languages and those are rather unfamiliar to these day’s programmers. In this thesis, the focus is on the comparison between diferent evaluation techniques but mostly focused on strict evaluation and lazy evaluation. First, the theoretical diference is presented in mathematical aspect in lambda calculus, and the practical examples are presented in Python and Haskell. The results show that a program can beneft lazy evaluation when evaluating non- terminable expressions or optimize the performance when the values are cached. However, in case the function has side efects, lazy evaluation cannot be used to- gether and it makes harder to predict the memory usage compared to strict evalu- ation. Keywords: evaluation strategy, lambda calculus, algorithm efciency, strict eval- uation, lazy evaluation, Haskell, Python The originality of this thesis has been checked using the Turnitin Originality Check service.
    [Show full text]
  • CS 251: Programming Languages Fall 2015 ML Summary, Part 5
    CS 251: Programming Languages Fall 2015 ML Summary, Part 5 These notes contain material adapted from notes for CSE 341 at the University of Washington by Dan Grossman. They have been converted to use SML instead of Racket and extended with some additional material by Ben Wood. Contents Introduction to Delayed Evaluation and Thunks .......................... 1 Lazy Evaluation with Delay and Force ................................. 2 Streams .................................................... 4 Memoization ................................................. 6 Integrating Lazy Evaluation into the Language ........................... 11 Introduction to Delayed Evaluation and Thunks A key semantic issue for a language construct is when are its subexpressions evaluated. For example, in ML (and similarly in Racket and most but not all programming languages), given e1 e2 ... en we evaluate the function arguments e2, ..., en once before we execute the function body and given a function fn ... => ... we do not evaluate the body until the function is called. This rule (\evaluate arguments in advance") goes by many names, including eager evaluation and call-by-value. (There is a family of names for parameter-passing styles referred to with call-by-.... Many are not particularly illuminating or downright confusing names, but we note them here for reference.) We can contrast eager evaluation with how if e1 then e2 else e3 works: we do not evaluate both e2 and e3. This is why: fun iffy x y z = if x then y else z is a function that cannot be used wherever
    [Show full text]
  • Programming Language Concepts Subroutines
    Programming Language Concepts Subroutines Janyl Jumadinova 23 February, 2017 Arguments are also called \actual parameters" (as opposed to \formal parameters" in the function definition) Arguments, Parameters 2/20 Arguments, Parameters Arguments are also called \actual parameters" (as opposed to \formal parameters" in the function definition) 2/20 Examples of Function Calls (Python) def f(a,b,c): ... return 100*a+10*b+c 3/20 I Named Arguments Examples of Function Calls (Python) def f(a=1,b=1,c=1): ... return 100*a+10*b+c I Default Parameter Values 4/20 Examples of Function Calls (Python) def f(a=1,b=1,c=1): ... return 100*a+10*b+c I Default Parameter Values I Named Arguments 4/20 Examples of Function Calls (Haskell) 5/20 Parameter Evaluation \Applicative Order" evaluation: arguments evaluated before the function call. \Eager" evaluation. 6/20 Parameter Evaluation \Normal Order" evaluation: arguments are not evaluated until they are needed (possibly never) 7/20 Parameter Evaluation \Lazy" evaluation: I arguments are evaluated at most once (possibly never). I Even though we used a Haskell example to illustrate \normal order", it is more accurate to call Haskell's evaluation order \lazy." I In normal order, a parameter could be evaluated more than once (i.e., evaluated each time it appears in the function). 8/20 Closures I In languages that support “first-class functions," a function may be a return value from another function; a function may be assigned to a variable. I This raises some issues regarding scope. 9/20 Closures 10/20 Another solution (used by JavaScript and most other statically-scoped languages): bind the variables that are in the environment where the function is defined.
    [Show full text]
  • Lazy and Eager Evaluation
    Functional Programming and Specification Lecture Note 1, 4 February 2011 Lazy and Eager Evaluation Recall that evaluation is “call by value” in ML: before performing function application, we have to evaluate the argument. This happens even if the argument isn’t needed for the result, as in fun f(y) = 1 Because of this, ML is called an eager language. Another terminology for essentially the same thing is that ML is strict; this means that applying f or any other function to an expression exp having no value (because exp fails to terminate) gives an expression that has no value. Some functional languages use lazy evaluation, also known as “call by need”, meaning that an expression will not be evaluated unless its value is actually required in order to produce the result. In a lazy language, f(exp) = 1, even if exp fails to terminate — the argument to f doesn’t need to be evaluated to determine the result. This isn’t done by analyzing the definition of f, but rather by delaying evaluation of the argument until its value is required. One can’t analyze functions in general to see if they use their arguments — one reason (not the only one!) is that in ML, any function might be the outcome of a complicated computation rather than just text. Not evaluating an unused argument saves time. If its evaluation doesn’t terminate, not evaluating it saves a lot of time! Here is another example: fun g(x,y,z) = if x<2 then y+3 else z+6 Depending on the value of x, either the value of y or the value of z will be required, but not both.
    [Show full text]
  • Functional Programming in Javascript Table of Contents
    Functional Programming in JavaScript Table of Contents Functional Programming in JavaScript Credits About the Author About the Reviewers www.PacktPub.com Support files, eBooks, discount offers and more Why Subscribe? Free Access for Packt account holders Preface What this book covers What you need for this book Who this book is for Conventions Reader feedback Customer support Downloading the example code Errata Piracy Questions 1. The Powers of JavaScript’s Functional Side – a Demonstration Introduction The demonstration The application – an e-commerce website Imperative methods Functional programming Summary 2. Fundamentals of Functional Programming Functional programming languages What makes a language functional? Advantages Cleaner code Modularity Reusability Reduced coupling Mathematically correct Functional programming in a nonfunctional world Is JavaScript a functional programming language? Working with functions Self-invoking functions and closures Higher-order functions Pure functions Anonymous functions Method chains Recursion Divide and conquer Lazy evaluation The functional programmer’s toolkit Callbacks Array.prototype.map() Array.prototype.filter() Array.prototype.reduce() Honorable mentions Array.prototype.forEach Array.prototype.concat Array.prototype.reverse Array.prototype.sort Array.prototype.every and Array.prototype.some Summary 3. Setting Up the Functional Programming Environment Introduction Functional libraries for JavaScript Underscore.js Fantasy Land Bilby.js Lazy.js Bacon.js Honorable mentions Development and
    [Show full text]