Activity Guide APIs and Using Functions with Parameters

Transcription

1 Unit 3 Lesson 5 Name(s) Period Date Activity Guide APIs and Using Functions with Parameters CS Content An API is a reference guide which catalogs and explains the functionality of a programming language. If a programmer develops the practice of referencing an API, she can make full use of that functionality without undergoing the tedium of memorizing every detail of the language. In today s lesson, you will read through the API in order to find and understand new commands for moving the turtle, selecting colors, and drawing different-sized dots and lines on the screen. You may not necessarily understand every command in the drawing API in detail, but you should be familiar with referencing the API as a standard part of the process of writing a program. Challenge 1: A new way to move The moveforward() turtle command that we've used so far moves the turtle the same amount every time (25 pixels in fact). Similarly, turnleft() turns the turtle to the left exactly 90 degrees. Today we are going to see how some functions can accept input, such as a number, to more exactly control behavior. For example, you can write moveforward(103) to move the turtle exactly 103 pixels if you like. How far is it to the top edge of the screen? Run the program to see the new version of moveforward() in action. Then changing only the number supplied to moveforward(), move the turtle to the top edge of the screen. Experiment to find out the distance in pixels between where the turtle starts and the top edge of the screen. Once you've found it, compare with a neighbor to see that you're seeing the same thing and click Finish to move on. NOTE: There might be slight differences depending on whether you get the turtle to just touch the edge, or go off the screen entirely. Challenge 2: Parameter When you have a command like: moveforward(100) we say that the moveforward() command accepts a parameter. And 100 is the value given or supplied to moveforward() 's parameter. Since this value can change, you will often see a written description for the command that looks something like moveforward(pixels) to indicate that the value supplied to moveforward() 's parameter should be the number of pixels you want it move. The good old moveforward() command still exists. In fact it's the same command as moveforward(pixels). The "parameter-less" version of moveforward() simply supplies a default value to the parameter. We might also say that the moveforward() command has an optional parameter since you could call either moveforward() or moveforward(50) and it doesn't cause an error when you run the program. NOTE: you can write your own functions that accept parameters, too! But we'll get to that in later lessons.

2 New Commands! Check it out. The turtle toolbox now contains the parameterized versions of the turtle commands including turnleft(angle) and turnright(angle). Notice that penup() and pendown() don't have parameters. Use the parameterized versions of the commands to draw a triangle with sides that are 100 pixels long. Challenge 3: Documentation As we move forward you are going to see more and more (and more!) commands added to the toolbox. What happens if you see a command and don't understand it, or you forget how it works? Don't worry, this happens to professional programmers all the time! No one actually memorizes long lists of commands. Most programming environments have ways to quickly look up documentation about the commands of the language you're using. Good news: App Lab has documentation too! When you hover your mouse over a command in the block palette a bubble pops up with a quick reminder of what a function does, and what its parameters are. If you click "See examples", you will be taken to more detailed documentation of the command which includes code examples that you can even copy and paste. More New Commands: Color and Width Two powerful new commands have been added to the toolbox, pencolor() and penwidth(). Read the documentation: Read through the documentation for pencolor() and penwidth() which let you set the color and size of the pen your turtle uses to draw. The documentation for pencolor() has a lot in it! For now just look at 2

3 the named colors, things like "red", "green", etc. Don't worry, you'll get a lot of opportunities to practice with colors in a variety of ways. We're just getting started! Draw the square: Use these functions to draw the thick blue square shown below. Challenge 4: Draw with Dots We've added a new command called dot(). Read the documentation for the dot() command. Make a "snowman" 1. Using whatever color you like, make a dot so big that it fills the screen. 2. In a different color, make 3 dots in a row, each one smaller than the next. (We made our dots white to look like a snowman) You might want to go back to the documentation for pencolor() to look up other colors to use. Challenge 5: Hexadecimal Colors In reading the documentation may have noticed that pencolor() can accept colors in the hexadecimal format (e.g. "#AC9100"). Colors on websites will often be represented in this format. It's useful to know how to interpret and use this format when trying to duplicate colors in your own images. Read the documentation: Review the documentation for pencolor() and pay particular attention to how to define colors in hexadecimal. Draw the bullseye: Draw the bullseye below using a combination of pencolor() and dot(). Hint: The sample image was created using three of the following hexadecimal colors: #00ABDC, #CC4400, #1188CC, #006699, #11CC00. Can you recall how hexadecimal color works to select the correct colors on your first try? Challenge 6: Multiple Parameters Making Arcs Many commands need more than one parameter to make sense. When a command needs more than one parameter, the parameters are separated by commas and the order of the parameters matters. Two new commands have been added to the block palette, arcleft() and arcright() which both accept two parameters. Read the documentation: Read the documentation for arcleft() and arcright(). 3

4 Draw a squiggly line: Using these new commands with the ones you have already learned draw a purple squiggle on a blue background. Feel free to use any of the methods for choosing colors you have already learned. Hint: all the parameters are multiples of 10, and the colors are from the following list of named colors: PowderBlue, LightBlue, Indigo, Purple, Magenta. Challenge 7: Transparency Red, Green, Blue, Alpha There is another command that lets you set the pen color called penrgb(r,g,b,a). The first 3 parameters are for values (in the range 0-255) for the red, green, and blue channels. The 4th parameter a stands for "alpha". The "alpha channel" for color lets you set the level of opacity as a decimal value between 0 and 1 - it is interpreted as a percentage, so 0.5 equates to 50% opaque. For example: penrgb(113, 102, 160, 0.5). Read the Documentation: To figure out how to use penrgb() go read the documentation, paying special attention to the syntax used to give a command multiple values. Draw the circles: Use penrgb() and dot() to draw two overlapping circles as shown in the image. Challenge 8: Moving Relative to the Screen The turtle commands we've seen so far move the turtle relative to the turtle's location and direction. If you want to get the turtle to a specific position on the screen using only moveforward() or turnleft(), you need to know the turtle's location beforehand. Two new commands in the toolbox help resolve this issue. moveto() moves the turtle to a location on the screen based on its X and Y coordinates. turnto() turns the turtle in a specific direction. Together these commands can make many drawings easier to complete. Read the documentation: Read the documentation for moveto() and turnto(). Pay specific attention to how the coordinate system is arranged in App Lab as it is different from what you might have seen in a math class. Draw the smiley: Use these new commands to help you draw the smiley face pictured below. 4

5 Challenge 9: The Full Turtle We've added a few more commands to the toolbox. At this point you have access to every turtle command provided by App Lab. As we've already seen with our exploration of functions you can combine these commands to create more complex functionality, but at the lowest level all of your code will be making use of the set of commands provided by App Lab. Code you write will always be based upon the commands that are provided by the programming language you are using. When several commands are provided in a logical chunk, like the set of turtle commands, we refer to them collectively as a library of functions. The total set of commands that a language provides access to is called the application program interface, or simply an API. As you gain more experience you will gain familiarity with the API for the language you are using, but you will still want to return to the API documentation from time to time to remind yourself what functionality a language offers. Congratulations, you've really come a long way as a turtle artist! Explore the documentation for any new commands you see and use your skills as both an artist and user of API documentation to draw something of your own choosing. You must incorporate functions, arcs, dots, colors, transparency, moveto, and turnto commands. Rubric: Does your artwork have: Feature Possible Points at least 2 functions 10 at least 1 arc 5 at least 1 dot 5 at least 3 different colors 15 at least 1 transparency 5 at least 2 moveto 10 at least 1 turnto 5 Total 55 Your Points Reflection: 1. Multiple Choice: What is an API? a. Abstract Programming Inheritance The idea that abstractions in languages get passed down in newer versions b. Artificial Parameter Intelligence The idea that function parameters should be intelligent enough to know what you want as a programmer c. Application Program Interface A well-documented library of functions provided in a programming language that helps to simplify complex programming tasks. d. Applied Power Implementation e. Abstract Parameter Interface 2. Multiple Choice: What is a function parameter? a. para-meter -- a measure of the distance between a function s conception and implementation. b. A way to give input to a function that controls how the function runs. c. A collection of commands that can be used in a programming language. d. Another name for the purpose of a function. e. A named memory location. 5

6 3. Free Response: It is said that functions with parameters generalize the behavior of a more specific command. Explain what this sentence means to you using the difference between turnleft() and turnleft(angle). 6