WEBVTT

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We've already looked at the While Loop

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but what we're going to look at now is a different form of

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looping structure called the For Loop.

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Now a distinct feature about the for loop

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is that it allows you to specify and control

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exactly how often a loop should run

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depending on what kind of

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sensors and inputs you're actually using

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to make this work you have to give it three 

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particular forms of information.

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The first thing is you have to give it

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some kind of counter or variable

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that is set up at the start, thats going to keep track of

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how often the loop has run.

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In any kind of loop you need some kind of test

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thats going to allow you to decide

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whether or not the loop should end

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and the third thing we have to do, again

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as you have already found with the while loop

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is you've to have some mechanism that changes the value

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of the counter that you're using 

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otherwise you'll never exit the loop

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lets look at how that works.

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To make this test work

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you can use logic expressions

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again these have been looked at before, 

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lets just reiterate then for a moment

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so we've got a greater than statement

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which test whether one side is greater than the other

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and its partner less than

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we can also test if something is

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greater than or equal a particular value

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or less than or equal to a particular value

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then we've got the particular test

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of being equals and again

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the actual logical test for if one side of the test

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is equal to the other is to use the double equal sign

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not the single one, equally important

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is the not equals sign

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these are the different ways that we can check

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whether one side

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matches or doesn't match another and then whether 

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the loop is true to continue.

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Here's the general layout of the for statement

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as you'd expect with any loop 

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its got a marker at the start the brace

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to see where the code that will be executed in 

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the loop is and a marker at the end

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to see where the loop should end

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the key differences that you have

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are that all the control

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is done inside this bracket after the for statement

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we specify what's the starting condition

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what check are we going to perform

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and then how were going to change

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the starting value everytime the loop runs

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also its worth noting there's no semi-colon

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at the end of the statement

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because its not actually the end of a statement

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the statement finishes down at the bottom of these braces

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which act in the same way a semi-colon would.

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Here's a small example

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we've already looked at this for the while statement

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so what we've got here, is we have to setup

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a variable first of all, which we're going to use

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and then just as the previous slide shows 

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we setup a starting condition

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that sets it to be zero at the start, we setup

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the condition to keep it in the loop so long as the value of i

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is less than five this loop will continue to run

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and then finally we have how i changes

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in this case we're using the standard increment command

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thats built in to the programming language

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and then we've got the actual operation 

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between these two braces

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and as you can see this particular case 

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is going to drive forward for half a second

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and do it five times

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so this loop will run five times

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for when the value of i is zero

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then when i is one, when i is two

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when i is three, when i is four

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and then once it goes through the loop again 

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and increments to i being five

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and exits the loop and continues on executing the code

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beyond the for loop

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and this just highlights the roles of these elements