84 lines
1.8 KiB
Markdown
84 lines
1.8 KiB
Markdown
# For
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Repeat code a preset number of times.
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### @parent js/language
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Repeat code a fixed number of times.
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### Block Editor
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The Block Editor *for* loop is different than the Touch Develop *for* loop in an important way. The above for loop will iterate *five* times, with the loop variable *i* taking on values 0, 1, 2, 3, and 4. The Touch Develop for loop shown below will iterate four times:
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```
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for (let k = 0; k < 4; k++) {
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}
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```
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### Touch Develop
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### ~hide
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```
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let upper = 5
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```
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### ~
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```
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for (let k1 = 0; k1 < upper; k1++) {
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// Add code to repeat here, also called the `loop body`
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}
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```
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where
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* `0` is initial value of the loop index variable `k`
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* the value of `k` increases by 1 after each execution of the `loop body`
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* `upper` is the number of times the loop body will repeat
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In other words, the index variable (`k`) starts at 0 and increases by 1 each time the `loop body` executes, until `k = upper`.
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### Example: count to 5
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The following example displays numbers 1 through 5 on the LED screen:
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```
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for (let i = 0; i < 5; i++) {
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basic.showNumber(i + 1, 100)
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basic.pause(500)
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}
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```
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### Example: draw a box
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The [LED screen](/microbit/device/screen) has a fixed number of rows and columns (5x5), which is ideal for a for loop. This example uses a for loop to turn on the LEDs along the edge of the screen, making a square.
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```
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for (let i1 = 0; i1 < 5; i1++) {
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led.plot(0, i1)
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led.plot(4, i1)
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led.plot(i1, 0)
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led.plot(i1, 4)
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basic.pause(500)
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}
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```
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### ~hint
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Want to exit a loop early? The [break](/microbit/js/break) statement exits a loop before the end value is reached.
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### ~
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### Lessons
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[looper](/microbit/lessons/looper), [strobe light](/microbit/lessons/strobe-light)
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### See also
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[while](/microbit/js/while), [break](/microbit/js/break), [if](/microbit/reference/logic/if)
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