WEBVTT

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In this demo I'm going to enter some expressions in the 

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CodePad and how they will be evaluated

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before I start I'm going to clear the CodePad

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because it still has some output from the previous demo.

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If I want to clear the CodePad, all I have to do

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is click compile and it clears.

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The expressions I enter are going to include some variables

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so lets declare those variables first

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I want to declare three Integer variables

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X, Y and Z.

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The expressions can contain values, 

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variables and operators

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I'm going to start with an expression 

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that contains a relational operator

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X is less than or equal to twelve

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note than when I enter an expression and 

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want it to be evaluated

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I don't include a semi-colon at the end.

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That expression evaluates to a

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boolean value of true.

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The next expression simply multiplies

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the three variables together

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and evaluates to an Integer value.

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The next one's a bit more complicated

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and in fact its built up from two other expressions

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the first one Y is greater than three

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is combined using a conditional operator

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the and operator

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with Y is less than ten

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and that evaluates to false, another boolean value.

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That expression will only be true

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if Y is greater than three and Y is less than ten

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in other words if Y is in the range four to nine.

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Lets try an expression that combines arithmetic operators

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X plus three times Y

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and that evaluates to forty two

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because of operator precedents

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the multiplication operator is applied before 

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the addition operator in this expression

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so three times Y is calculated first

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and then twelve the value of X is added onto that.

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If we want the addition to be done first

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we have to enclose that part of the expression

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X plus three in brackets and then multiply

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and that evaluates to a different result.

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Finally lets try one of the increment operators

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this expression increments the value of X

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and gives the incremented value now 13.

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Note that unlike in the previous expressions

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this operator has actually changed the value 

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of the variable that its applied to

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and if I tried to see the value of X again

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I can see that it has actually changed to thirteen.