145 lines
3.6 KiB
Markdown
145 lines
3.6 KiB
Markdown
# Local Variables
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How to define and use local variables.
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### @parent language
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A variable is a place where you can store and retrieve data. Variables have a name, a [type](/js/types), and value:
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* *name* is how you'll refer to the variable
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* *type* refers to the kind of data a variable can store
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* *value* refers to what's stored in the variable
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### `var` and `let` statement
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Use the Touch Develop *var* statement to create a local variable and the [assignment operator](/reference/variables/assign) `=` to store something in the variable.
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For example, this code stores the number `2` in the `num1` variable:
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```
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let num1 = 2
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```
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Here's how to define a variable in the Touch Develop editor:
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1. Click `var`.
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2. Change the default variable name if you like.
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3. Click on the right-side of the [assignment operator](/reference/variables/assign) `:=` and type or click what you want to store in the variable.
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The resulting code should look something like this:
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// string variable
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```
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let name = "Mike"
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```
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// number variable
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```
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let counter = 1
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```
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// boolean variable
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```
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let bool = true
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```
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// image variable
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```
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let img = images.createImage(`
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. . # . .
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. # # # .
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# # # # #
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. # # # .
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. . # . .
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`)
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```
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See [Image](/reference/image/image) for info on creating and using image variables.
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### Store in var button
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Another way to define a variable is to use the `store in var` button. Here's how:
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* in the [Touch Develop editor](/js/editor), click a function button that returns a value (i.e. `led` `->` `brightness`)
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* click `store in var`
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* click `rename` to change the default variable name
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The resulting code should look something like this:
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```
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let brightness = led.brightness()
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```
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A variable is created for the number returned by the [brightness](/reference/led/brightness) function.
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### Using variables
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Once you've defined a variable, just use the variable's name whenever you need what's stored in the variable. For example, the following code shows the value stored in `counter` on the LED screen:
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```
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basic.showNumber(counter, 100)
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```
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To change the contents of a variable use the assignment operator `:=`. The following code sets `counter` to 1 and then increments `counter` by 10:
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```
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counter = 1
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counter = counter + 10
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```
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### Why use variables?
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Variables help simplify your code. For example, instead of turning on LEDs one by one like this:
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```
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led.plot(0, 0)
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led.plot(1, 1)
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led.plot(2, 2)
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led.plot(3, 3)
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led.plot(4, 4)
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```
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You can use a variable (`i`) and a [for loop](/reference/loops/for) to plot the same series of points (`i` is incremented by 1, each time the loop repeats):
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```
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for (let i = 0; i < 5; i++) {
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led.plot(i, i)
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}
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```
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### Local vs global variables
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Local variables exist only within the function or block of code where they're defined. Local variables don't exist outside of where they're defined. For example:
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```
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if (led.brightness() > 127) {
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let y = 1
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// `y` variable exists here
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} else {
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// `y` variable does not exist here
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}
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```
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Use [global variables](/js/data) when you need to access a variable in nested code blocks or across multiple functions.
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#### Notes
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* You can use the default variable names if you'd like, however, it's best to use descriptive variable names. To change a variable name in the editor, select the variable and then click `rename`.
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* Be careful not to confuse the assignment `:=` operator with the equals `=` operator.
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### Lessons
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[guess the number](/lessons/guess-the-number), [digi yoyo](/lessons/digi-yoyo), [rock paper scissors](/lessons/rock-paper-scissors), [love meter](/lessons/love-meter)
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### See also
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[global variables](/js/data), [types](/js/types), [assignment operator](/reference/variables/assign)
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