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I was wondering how to write a code that would do this, WITHOUT using IF and ELSE: when the button is pressed, one LED is on and the other one is off, but when the button is not pressed, the LED that was on turns off and the other one turns on.

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  • Other than with the ! operator?
    – Ignacio Vazquez-Abrams
    May 5, 2016 at 10:41
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    Commenting instead of replying because you asked for code, but this could be done in hardware. If you wire in a PNP transistor to switch the second LED, it will free up the second DIO pin.
    – KJP
    May 5, 2016 at 16:06
  • Can I ask why you don't want to use if and else? Is this just hypothetical fun?
    – Zach Mierzejewski
    May 5, 2016 at 16:37
  • @KJP if you add an x amount of shift registers, you'll free up an (x*8)-6 amount of in/outputs? ;D
    – Paul
    May 16, 2016 at 19:53

2 Answers 2

Reset to default
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Just use the return value of digitalRead (which is 1 or 0) as the input to digitalWrite:

int btnVal = digitalRead(3);
digitalWrite(4, btnVal);      // On when button is HIGH
digitalWrite(5, 1 - btnVal);  // Off when button is HIGH

Or using boolean instead:

bool btnVal = digitalRead(3);
digitalWrite(4, btnVal);      // On when button is HIGH
digitalWrite(5, !btnVal);     // Off when button is HIGH
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  • You can also use ! with int values.
    – Kroltan
    May 5, 2016 at 14:26
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    You don't say....
    – Majenko ♦
    May 5, 2016 at 14:27
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    Wasn't necessarily telling that to you, but leaving that comment as a note to the OP, which seems to be a beginner, or to any future reader.
    – Kroltan
    May 5, 2016 at 15:03
  • in C, bool and int are interchangeable.
    – rkosegi
    May 5, 2016 at 16:36
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    @EdgarBonet It may be called a _Bool but it's still an integer: Boolean values still behave as integers, can be stored in integer variables, and used anywhere integers would be valid, including in indexing, arithmetic, parsing, and formatting. This approach ("Boolean values are just integers") has been retained in all later versions of C.
    – Majenko ♦
    May 16, 2016 at 10:39
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You could do it with only a switch/case statement. You do not even need to de-bounce the switch.

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