We’re going to look at how our computers read and interpret computer files. We’ll talk about how some popular file formats like txt, wave, and bitmap are encoded and decoded giving us pretty pictures and lifelike recordings from just strings of 1’s and 0’s, and we’ll discuss how our computers are able to keep all this data organized and readily accessible to users. You’ll notice in this episode that we’re starting to talk more about computer users, not programmers, foreshadowing where the series will be going in a few episodes.
This video will talk about how we organize the data we use on our devices. You might remember last episode, Intro to Algorithms: Crash Course Computer Science #13, we walked through some sorting algorithms, but skipped over how the information actually got there in the first place! And it is this ability to store and access information in a structured and meaningful way that is crucial to programming. From strings, pointers, and nodes, to heaps, trees, and stacks, get ready for an ARRAY of new terminology and concepts.
So, we’ve talked about computer memory a couple of times in this series, but what we haven’t talked about is storage. Data written to storage, like your hard drive, is a little different because it will still be there even if the power goes out - this is known as non-volatile memory. Today we’re going to trace the history of these storage technologies from punch cards, delay line memory, core memory, magnetic tape, and magnetic drums, to floppy disks, hard disk drives, CDs, and solid-state drives. Initially, volatile memory, like RAM was much faster than these non-volatile storage memories, but that distinction is becoming less and less true today.
In this lesson, students are introduced to the string data type as a way of representing arbitrary sequences of ASCII characters. They will use strings to accept input from a user as they work on mastering two new UI elements, the text input, and the text area. Students combine these skills to develop a simple Mad Libs® app.
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Students will be able to:- identify strings as a unique data type which contains a sequence of ASCII characters.- describe the characteristics of the string data type.- accept string input in a program.- manipulate user-generated string input to generate dynamic output.
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This lesson introduces arrays as a means of storing lists of information within a program. The class begins by highlighting the difficulties that arise when trying to store lists of information in a variable. Students then watch a short video introducing arrays and a subset of the operations that can be performed with them. Students will work in Code Studio for the remainder of the class as they practice using arrays in their programs. At the conclusion of the sequence, students build a simple app which can be used to store and cycle through a list of their favorite things. In the next lesson, students will continue working with a version of this app that can display images and not just text strings.
Students will be able to:- identify an array as a data structure used to store lists of information in programs.- create arrays and access information stored within them using an index.- manipulate an array using the append, insert, and remove operations.- account for the fact that JavaScript arrays are zero-indexed when using them in a program.
This lesson will probably take two days to complete. It introduces students to algorithms that process lists of data. The students will do two unplugged activities related to algorithms and program some of them themselves in App Lab. The for loop is re-introduced to implement these algorithms because it’s straightforward to use to process all the elements of a list. The lesson begins with an unplugged activity in which students write an algorithm to find the minimum value in a hand of cards. Students then move to Code Studio to write programs that use loops and arrays. Students are shown how to use a for loop to visit every element in an array. Students use this pattern to process an array in increasingly complex ways. At the end of the progression, students will write functions which process arrays to find or alter information, including finding the minimum value - a problem they worked on in the unplugged activity. Finally, an unplugged activity has students reason about linear vs. binary search and attempt to write pseudocode for a binary search.
Students will be able to:- use a for loop in a program to implement an algorithm that processes all elements of an array.- write code that implements a linear search on an unsorted array of numbers.- write code to find the minimum value in an unsorted list of numbers.- explain how binary search is more efficient than linear search but can only be used on sorted lists.
Students continue to practice working with arrays and are introduced to a new user interface element, the canvas. The canvas includes commands for drawing simple geometric shapes (circles, rectangles, lines) and also triggers mouse and key events like any other user interface element. Over the course of the lesson, students combine these features to make an app that allows a user to draw an image while recording every dot drawn on the canvas in an array. By processing this array in different ways, the app will allow students to redraw their image in different styles, like random, spray paint, and sketching. Along the way, students use their knowledge of functions with return values to make code which is easy to manage and reuse.
Students will be able to:- programmatically control the canvas element in response to user interactions.- maintain a dynamically generated array through the running of a program in order to record and reuse user input.- use nested loops within a program to repeat a command on the same array index multiple times.- perform variable arithmetic within an array index to access items in an array by their relative position.
