Ejemplos > Estructuras de control

Declaración If (estructura condicional)

La declaración If es la estructura de control más básica de todas. Te permite hacer algo o no sólo si se cumple una condición (si es verdadera). Se escribe así:

   // hace cosas si la condición es verdad

Existe una variación llamada if-else que se escribe:

   // hace cosas si la condición es cierta

   // hace cosas si la condición es falsa

Todavía queda el else-if, en la que se comprueba una segunda condición en caso de que la primera sea falsa:

   // hace cosas si la condición es cierta

   // hace cosas sólo si la primera condición es falsa
   // y la segunda es cierta

Usarás la declaración If todo el tiempo. El ejemplo siguiente enciende un LED conectado al pin 13 (el LED incorporado en la placa en muchos Arduinos) si el valor leído en la entrada analógica supera cierto valor.

Circuito

click en la imagen para aumentar

imagen creada usando Fritzing. Para más ejemplos de circuitos, ver la página del proyecto Fritzing

Esquema:

click en la imagen para aumentar

Código

 (:includeurl http://arduino.googlecode.com/svn/trunk/build/shared/examples/Control/IfStatementConditional/IfStatementConditional.pde border=0:)

 (:includeurl http://arduino.googlecode.com/svn/trunk/build/shared/examples/Control/ifStatementConditional/ifStatementConditional.pde border=0:)

   pinMode(ledPin, OUTPUT);

image developed using Fritzing. For more circuit examples, see the Fritzing project page

(:div class=code :)

 /*
   Conditionals - If statement
  
  This example demonstrates the use of if() statements.
  It reads the state of a potentiometer (an analog input) and turns on an LED
  only if the LED goes above a certain threshold level. It prints the analog value
  regardless of the level.
  
  The circuit:
  * potentiometer connected to analog pin 0.
  Center pin of the potentiometer goes to the analog pin.
  side pins of the potentiometer go to +5V and ground
  * LED connected from digital pin 13 to ground
  
  * Note: On most Arduino boards, there is already an LED on the board
  connected to pin 13, so you don't need any extra components for this example.
  
  created 17 Jan 2009
  by Tom Igoe
  
   http://arduino.cc/en/Tutorial/IfStatement
  
  */

 // These constants won't change:
 const int analogPin = 0;     // pin that the sensor is attached to
 const int ledPin = 13;       // pin that the LED is attached to
 const int threshold = 400;   // an arbitrary threshold level that's in the range of the analog input

 void setup() {
   // initialize the LED pin as an output:
   pinMode(LED, OUTPUT);
   // initialize serial communications:
   Serial.begin(9600);
 }

 void loop() {
   // read the value of the potentiometer:
   int analogValue = analogRead(analogPin);

   // if the analog value is high enough, turn on the LED:
   if (analogValue > threshold) {
     digitalWrite(ledPin, HIGH);
   } 
   else {
     digitalWrite(ledPin,LOW); 
   }

   // print the analog value:
   Serial.println(analogValue, DEC);

 }

(:divend:)

Examples > Control Structures

If Statement (Conditional Statement)

The If statement is the most basic of all programming control structures. It allows you to make something happen or not depending on whether a given condition is true or not. It looks like this:

if (someCondition) {
   // do stuff if the condition is true
}

There is a common variation called if-else that looks like this:

if (someCondition) {
   // do stuff if the condition is true
} else {
   // do stuff if the condition is false
}

There's also the else-if, where you can check a second condition if the first is false:

if (someCondition) {
   // do stuff if the condition is true
} else if (anotherCondition) {
   // do stuff only if the first condition is false
   // and the second condition is true
}

You'll use if statements all the time. The example below turns on an LED on pin 13 (the built-in LED on many Arduino boards) if the value read on an analog input goes above a certain threshold.

Circuit

click the image to enlarge

Schematic:

click the image to enlarge

Code

/*
  Conditionals - If statement

 This example demonstrates the use of if() statements.
 It reads the state of a potentiometer (an analog input) and turns on an LED
 only if the LED goes above a certain threshold level. It prints the analog value
 regardless of the level.

 The circuit:
 * potentiometer connected to analog pin 0.
 Center pin of the potentiometer goes to the analog pin.
 side pins of the potentiometer go to +5V and ground
 * LED connected from digital pin 13 to ground

 * Note: On most Arduino boards, there is already an LED on the board
 connected to pin 13, so you don't need any extra components for this example.

 created 17 Jan 2009
 by Tom Igoe

  http://arduino.cc/en/Tutorial/IfStatement

 */

// These constants won't change:
const int analogPin = 0;     // pin that the sensor is attached to
const int ledPin = 13;       // pin that the LED is attached to
const int threshold = 400;   // an arbitrary threshold level that's in the range of the analog input

void setup() {
  // initialize the LED pin as an output:
  pinMode(LED, OUTPUT);
  // initialize serial communications:
  Serial.begin(9600);
}

void loop() {
  // read the value of the potentiometer:
  int analogValue = analogRead(analogPin);

  // if the analog value is high enough, turn on the LED:
  if (analogValue > threshold) {
    digitalWrite(ledPin, HIGH);
  } 
  else {
    digitalWrite(ledPin,LOW); 
  }

  // print the analog value:
  Serial.println(analogValue, DEC);

}