CS320n –Visual Programming Definite / Counted Loops (Slides 7-1) Thanks to Wanda Dann, Steve Cooper, and Susan Rodger for slide ideas.

Visual ProgrammingDefinite / Counted Loops2 What We Will Do Today Learn how what definite loops are and how to use them in a program

Visual ProgrammingDefinite / Counted Loops3 Repetition In many kinds of animations, especially simulations and games, some actions happen again and again. – Example: Gallery games where targets appear randomly on screen and are caught or shot down, only to appear elsewhere in the scene Actions are made to happen again and again by running an animation instruction (or a method) more than once

Visual ProgrammingDefinite / Counted Loops4 Computers are Fast This is why we use computers. The number of instructions a CPU can carry out is mind boggling –Intel Processor: 3.20 gigahertz. –CPU doing 3,200,000,000 instructions per second. –Simple instructions like adding two numbers, looking up the value of a variable Lots of simple instructions can so quickly can accomplish a lot –3D animations, working with DNA, complex simulations.

Visual ProgrammingDefinite / Counted Loops5 Example A bunny sneaks into a garden and wants to eat the broccoli. The bunny will need to hop several times to get to the broccoli.

Visual ProgrammingDefinite / Counted Loops6 bunny.hop

Visual ProgrammingDefinite / Counted Loops7 bunny.hop Makes bunny hop up and down, making a sound and traveling forward 0.8 meters Code on next slide How do we get the bunny to hop enough times to get over to the broccoli?

Visual ProgrammingDefinite / Counted Loops8 One solution Does this work? Are there any problems with it?

Visual ProgrammingDefinite / Counted Loops9 Counted Loop A counted loop is an alternative way to repetitive code Repeats instructions a counted number of times One of the commands available in Alice

Visual ProgrammingDefinite / Counted Loops10 Code for Loops The loop instruction executes a definite number of times, specified by a count. (Set when insert loop) Using a loop instruction – saves time when coding – is convenient, easy to change count –can use a function that returns a number in place of the count

Visual ProgrammingDefinite / Counted Loops11 Modify the Bunny Animation Make the bunny hop over to a broccoli and eat it Then hop to next broccoli and eat it move broccoli so not all together only do with 3 broccoli –fairly easy to expand to more broccoli

Visual ProgrammingDefinite / Counted Loops12 Infinity times… If “Infinity times” is selected for a loop, this means the loop will run until the program is shut down

Visual ProgrammingDefinite / Counted Loops13 Example 1: Add a bunny Add a bunny to the broccoli scene this bunny should jump up and down while the other bunny eats all the broccoli

Visual ProgrammingDefinite / Counted Loops14 Does this Work?

Visual ProgrammingDefinite / Counted Loops15 How Do We fix This? Get both bunnies to move –one definitely (the one that eats the broccoli) –one indefinitely (the one that hops up and down until the movie stops?)

Visual ProgrammingDefinite / Counted Loops16 Example 2: Carousel To make the carousel go round continuously in an amusement park world:

Visual ProgrammingDefinite / Counted Loops17 More complicated loops What can be placed in a loop? –any number of other commands –including other loops –a loop within a loop –this is a called a nested loop Example in book: a double ferris wheel

Visual ProgrammingDefinite / Counted Loops18 An example of nested loops The whole Ferris wheel will rotate clockwise, while the two inner wheels will rotate counterclockwise. The inner wheels should perform 2 revolutions for each outer loop revolution.

Visual ProgrammingDefinite / Counted Loops19 Rotating each of the wheels Rotating the outer wheel 10 times Rotating the inner wheels 2 times

Visual ProgrammingDefinite / Counted Loops20 The Complete Program The two loops structures, inner wheel loop nested within the outer wheel loop. How many times does the inner loop execute?

Visual ProgrammingDefinite / Counted Loops21 Using a Function for Count A loop count can be computed by calling a function that returns a number value. The loop instruction automatically rounds the returned value to the nearest whole number.