Operators That Add and Subtract
These seem simple at first but there are a few surprises.
The Additive Operators¶
In math, additive refers to both addition and subtraction. You can think of subtraction as just adding with negative numbers.
The plus sign +
is used for math addition and string concatenation.
The minus sign 
is used for math subtraction.
Using the Additive Operators¶
Adding and Subtracting Directly into Variables.¶
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Adding and Subtracting with Variables¶
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Concatenation of strings.¶
The plus sign +
is also used for concatenation
Concatenation, or combining string to form a new longer string. Notice that the <br />
tags are being concatenated too.
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Concatenation of Strings and Numbers.¶
When the plus sign has one string to its left OR right and a number on the other side, the number will be converted to a string and concatenated to the string.
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Concatenation when you don't expect it!.¶
When you have a string that contains just numbers and you try to add it to a true number JavaScript will concatenate it and not do addition.
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Converting from a string to a number.¶
When you have a string that contains a valid number, you can convert it to a number. We use the Number()
function for this.
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New Coding Standard
Refer to the Coding standards regarding specifics
Note standards regarding caclulations and the use of document.write
Labs
 Lab04: Additive Operators
 unit02/labs/lab04additiveOperators.html
Exercises
 Exercise for lab04
 unit02/exercises/exercise04.html