Software failures happen all the time. Sometimes it’s a little bug that makes a program difficult to use; other times an error might crash your entire computer. Some software failures are more spectacular than others.
In 1996, The ARIANE 5 rocket of the European Space Agency was launched for its first test flight: Countdown, ignition, flame and smoke, soaring rocket... then BANG! Lots of little pieces scattered through the South American rainforest. Investigators had to piece together what happened and finally tracked down this tiny, irrelevant bug. A piece of software onboard the rocket which was not even needed had reported a value that was too big to be stored. An error was stored instead, but other software interpreted the error as saying the rocket was 90 degrees off course. Thankfully, no one was on board but the failure still caused about $370 million of damage.
Software engineering is all about how we can create software despite this enormous size and complexity while hopefully get a working product in the end. It was first introduced as a topic of computer science in the 1960s during the so-called "software crisis" when people realized that the capability of hardware was increasing at incredible speeds while our ability to develop software is staying pretty much the same.
As the name software engineering suggests, we are taking ideas and processes from other engineering disciplines (such as building bridges or computer hardware) and applying them to software. Having a structured process in place for developing software turns out to be hugely important because it allows us to manage the size and complexity of software. As a result of advances in software engineering, there are many success stories of large and complex software products that work well and contain few bugs. For example, Google's huge projects (Google search, Gmail, etc.) are built by teams of thousands of engineers, yet they still manage to create software that does what it should.
People often become frustrated with computers and other digital devices. At some point when using these devices, you are likely to become annoyed that the system did something you didn't want it to do, or you can't figure out how to get the computer to do what you want, but why is that? Humans made computers, so why are computers often so frustrating for humans to use?
Human-computer interaction (HCI) is about trying to make programs useful, usable, and accessible to humans. It goes way beyond choosing layouts, colors, and fonts for an interface. It's strongly influenced by the psychology of how people interact with digital devices, which means understanding many issues about how people behave, how they perceive things, and how they understand things so that they feel that a system is working to help them and not hinder them. By understanding HCI, developers are more likely to create software that is effective and popular. If you ask people if they have ever been frustrated using a computer system, you’ll probably get a clear message that HCI isn’t always done well.
This chapter explores user interfaces, usability, and overall user experience with technology.
This lesson presents a top-down problem-solving strategy for designing solutions to programming problems. Students use a worksheet to learn about top-down design, and then on paper, design a solution to a new turtle drawing challenge with a partner. Having practiced this approach on paper and in code, students will be presented again with the 3x3 square challenge from an earlier lesson and asked to improve upon their old solution by designing multiple layers of functions.
Students will be able to:- write a complete program with functions that solve sub-tasks of a larger programming task.- explain how functions are an example of abstraction.- use a “top-down” problem-solving approach to identify sub-tasks of a larger programming task.
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In this lesson, students add variables to two different exemplary apps to keep track of a score or a count of some number of button clicks. The major topic is variable in scope and understanding the differences, benefits, and drawbacks, of using global versus local variables. This lesson focuses more on using global variables since in event-driven apps that’s what you need to keep track of data across multiple events.
The very basics of a simple if statement are also presented in this lesson, mostly to highlight the difference between the = and == operators. Finally, students are asked to apply what they’ve learned about variables, scope, and if statements, to make their own “clicker” game modeled after one of the exemplars they saw during the lesson.
Students will be able to:- use global variables to track numeric data in an app.- give a high-level explanation of what “variable scope” means.- debug problems related to variable scoping issues.- modify existing programs to add and update variables to track information.- create a multi-screen "clicker" game from scratch.
This lesson attempts to walk students through the iterative development process of building an app (basically) from scratch that involves the use of if statements. Following an imaginary conversation between two characters - Alexis and Michael - students follow the problem solving and program design decisions they make for each step of constructing the app. Along the way, they decide when and how to break things down into functions, and of course, discuss the logic necessary to make a simple game.
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The last step - writing code that executes an end-of-game condition - students must do on their own. How they decide to use if statements to end the game will require some creativity. The suggested condition - first to score 10 points - is subtly tricky and can be written in many different ways.
At the conclusion of the lesson, there is three practice Create PT-style questions as well as resources explaining the connection between this lesson and the actual Create PT. Depending on how you use these materials they can easily add an additional day to this lesson.
Students will be able to:- write code to implement solutions to problems from pseudocode or description.- follow the iterative development process of a collaboratively created program.- develop and write code for conditional expressions to incorporate into an existing program.- write a large program from scratch when given directions for each step.
Students will extend the My Favorite Things app they built in the previous lesson so that it now manages and displays a collection of images and responds to key events. Students are introduced to the practice of refactoring code in order to keep programs consistent and remove redundancies when adding new functionality. As part of learning to use key events, students are shown that event handlers pass a parameter which contains additional information about the event. This lesson also serves as further practice at using arrays in programs.
Students will be able to:- use an array to maintain a collection of data in a program.- create apps that allow user interaction through key events.- refactor code in order to appropriately incorporate new functionality while maintaining readability and consistency.
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.
