{"id":89,"date":"2019-10-22T08:37:40","date_gmt":"2019-10-22T08:37:40","guid":{"rendered":"https:\/\/starthardware.org\/en\/?p=89"},"modified":"2019-10-22T08:37:41","modified_gmt":"2019-10-22T08:37:41","slug":"unit-12-the-button-and-the-if-statement","status":"publish","type":"post","link":"https:\/\/starthardware.org\/en\/unit-12-the-button-and-the-if-statement\/","title":{"rendered":"Unit 12 \u2013 The Button and the if-Statement"},"content":{"rendered":"\n

This program should switch a LED when a button is pressed and switch off when it is not pressed any more. I suggest, we start with the Blink example code.<\/p><\/blockquote>\n\n\n\n

Did you build the circuit of Unit 11<\/a>?<\/p>\n\n\n\n

\"Arduino<\/figure>\n\n\n\n

Here comes the code:<\/p>\n\n\n\n

int ledPin = 9;\n\nvoid setup(){\n  pinMode(ledPin,OUTPUT);\n}\n\nvoid loop(){\n  digitalWrite(ledPin, HIGH);\n  delay(200);\n  digitalWrite(ledPin, LOW);\n  delay(200);\n}<\/code><\/pre>\n\n\n\n
You already know the program from Unit 7<\/a>. Now let\u2019s rearrange it.<\/p>\n\n\n\n
I suggest to store the pin number where the is connected to in a variable.<\/p>\n\n\n\n
int buttonPin = 11;<\/code><\/pre>\n\n\n\n
Now, we have to tell Arduino that we want to use a pin as an input. The command is:<\/p>\n\n\n\n
pinMode(buttonPin,INPUT);<\/code><\/pre>\n\n\n\n
You realized it, yes? It is the same command we used for the LED. Just the argument this time is not OUTPUT but INPUT.<\/p>\n\n\n\n
To find out whether the button is pushed (HIGH) or not (LOW) we can use this command:<\/p>\n\n\n\n
digitalRead(buttonPin);<\/code><\/pre>\n\n\n\n
Until now, we just used commands without returning results. This one is doing it. When we use it it returns HIGH or LOW. It is called a return value.<\/p>\n\n\n\n
That is a bit hard to get. Imagine, there would be a command (or better a method) which is called sum(a,b). The arguments a and b are two numbers which should be calculated as a sum. The return of our command would be the result of the calculation. To store the result, we use another variable. This looks like that: c = summe (a,b); Now the result is stored in the variable c.<\/p>\n\n\n\n
The command digitalRead(buttonPin); returns either HIGH or LOW. But how can we find out what it is? Therefore we are using on of the most important constructions in programming: the if-statement.<\/p>\n\n\n\n
The if-Statement<\/h3>\n\n\n\n
Using the if-statement we can find out whether a condition is true of false. Let\u2019s assume you have red and blue building bricks and you want to sort by color them into two boxes. How would you do that?<\/p>\n\n\n\n
\"Arduino<\/figure>\n\n\n\n
Maybe like that:<\/p>\n\n\n\n
  1. take a brick<\/li>
  2. check if it is red<\/li>
  3. if it is red put it in box A<\/li><\/ol>\n\n\n\n
    And this is exactly who to use the if-statement. Easy, isn\u2019t it? This is how to write it. Look to it that we use two equality signs. That is very important.<\/p>\n\n\n\n
    if (brick==red) {\n  put brick in box A\n}<\/code><\/pre>\n\n\n\n
    Great. Now we can put all the red bricks into box A. But the blue ones would remain on the floor. How can we put them into box B? A suggestion:<\/p>\n\n\n\n
    1. take a brick<\/li>
    2. check if it is red<\/li>
    3. if it is red put it in box A<\/li>
    4. else put it in box B<\/li><\/ol>\n\n\n\n
      Great, no? And this is how it is programmed:<\/p>\n\n\n\n
      if (brick==red) {\n put brick in box A\n} else {\n put brick in box B\n}<\/code><\/pre>\n\n\n\n
      \"Arduino<\/figure>\n\n\n\n
      Did you saw the green brick? It also lands in box B because we are not asking for blue but for not red<\/em>. \ud83d\ude09<\/p>\n\n\n\n
      But back to our program. This looks like that and need to be changed:<\/p>\n\n\n\n
      int ledPin = 9;\nint buttonPin = 11;\n\nvoid setup(){\n  pinMode(ledPin,OUTPUT);\n  pinMode(buttonPin,INPUT);\n}\n\nvoid loop(){\n  digitalWrite(ledPin, HIGH);\n  delay(200);\n  digitalWrite(ledPin, LOW);\n  delay(200);\n}<\/code><\/pre>\n\n\n\n
      The if statement for the button asks if the button is HIGH:<\/p>\n\n\n\n
      if (digitalRead(buttonPin)==HIGH){\n\n}<\/code><\/pre>\n\n\n\n
      If the button is HIGH the LED should be turned on:<\/p>\n\n\n\n
      if (digitalRead(buttonPin)==HIGH){\n  digitalWrite(ledPin, HIGH);\n}<\/code><\/pre>\n\n\n\n
      Otherwise (else) it should be turned off:<\/p>\n\n\n\n
      if (digitalRead(buttonPin)==HIGH){\n  digitalWrite(ledPin, HIGH);\n} else {\n  digitalWrite(ledPin, LOW);\n}<\/code><\/pre>\n\n\n\n
      The whole program looks like that:<\/p>\n\n\n\n
      int ledPin = 9;\nint buttonPin = 11;\n\nvoid setup(){\n  pinMode(ledPin,OUTPUT);\n  pinMode(buttonPin,INPUT);\n}\n\nvoid loop(){\n  if (digitalRead(buttonPin)==HIGH){\n    digitalWrite(ledPin, HIGH);\n  } else {\n    digitalWrite(ledPin, LOW);\n  }\n}<\/code><\/pre>\n\n\n\n
      Does it work? Super! Now try to change the program in that way that the LED is turns off when the button is pressed. You can find the solution here:<\/p>\n\n\n\n
      Solution<\/p>\n\n\n\n
      Of course there are a lot of possible solutions. Here are two:<\/p>\n\n\n\n
      int ledPin = 9;\nint buttonPin = 11;\n\nvoid setup(){\n  pinMode(ledPin,OUTPUT);\n  pinMode(buttonPin,INPUT);\n}\n\nvoid loop(){\n  if (digitalRead(buttonPin)==LOW){\n    digitalWrite(ledPin, HIGH);\n  } else {\n    digitalWrite(ledPin, LOW);\n  }\n}<\/code><\/pre>\n\n\n\n
      Or:<\/p>\n\n\n\n
      int ledPin = 9;\nint buttonPin = 11;\n\nvoid setup(){\n  pinMode(ledPin,OUTPUT);\n  pinMode(buttonPin,INPUT);\n}\n\nvoid loop(){\n  if (digitalRead(buttonPin)==HIGH){\n    digitalWrite(ledPin, LOW);\n  } else {\n    digitalWrite(ledPin, HIGH);\n  }\n}<\/code><\/pre>\n\n\n\n
      That was not so easy. Great, that you managed it anyway. Now you know the most important things of programming: variables<\/strong>,\u00a0loops<\/strong>\u00a0and the\u00a0if statement<\/strong>. Keep it up! From now on it get\u2019s easier. Promise!<\/p><\/blockquote>\n","protected":false},"excerpt":{"rendered":"
      This program should switch a LED when a button is pressed and switch off when it is not pressed any more. I suggest, we start with the Blink example code. Did you build the circuit of Unit 11? Here comes the code: You already know the program from Unit 7. Now let\u2019s rearrange it. I… Read More »Unit 12 \u2013 The Button and the if-Statement<\/span><\/a><\/p>\n","protected":false},"author":1,"featured_media":92,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"neve_meta_sidebar":"","neve_meta_container":"","neve_meta_enable_content_width":"","neve_meta_content_width":0,"neve_meta_title_alignment":"","neve_meta_author_avatar":"","neve_post_elements_order":"","neve_meta_disable_header":"","neve_meta_disable_footer":"","neve_meta_disable_title":"","footnotes":""},"categories":[2],"tags":[],"class_list":["post-89","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-arduino-tutorial"],"yoast_head":"\nUnit 12 \u2013 The Button and the if-Statement - StartHardware - Tutorials for Arduino<\/title>\n<meta name=\"robots\" content=\"index, follow, max-snippet:-1, max-image-preview:large, max-video-preview:-1\" \/>\n<link rel=\"canonical\" href=\"https:\/\/starthardware.org\/en\/unit-12-the-button-and-the-if-statement\/\" \/>\n<meta property=\"og:locale\" content=\"en_US\" \/>\n<meta property=\"og:type\" content=\"article\" \/>\n<meta property=\"og:title\" content=\"Unit 12 \u2013 The Button and the if-Statement - StartHardware - Tutorials for Arduino\" \/>\n<meta property=\"og:description\" content=\"This program should switch a LED when a button is pressed and switch off when it is not pressed any more. 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