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if

Description

The if statement checks for a condition and executes the proceeding statement or set of statements if the condition is 'true'.

Syntax

if (condition) { // statement(s) }

Note

  • If there is only one statement inside if, the brackets can be omitted.
  • If there are two or more statements, the brackets MUST be used. If not, only the first statement is belong to if.
if (x > 120) digitalWrite(LEDpin, HIGH); if (x > 120) digitalWrite(LEDpin, HIGH); if (x > 120) {digitalWrite(LEDpin, HIGH);} if (x > 120) { digitalWrite(LEDpin1, HIGH); digitalWrite(LEDpin2, HIGH); } // all are correct

Parameter Values

  • condition: a boolean expression (i.e., can be true or false).

Example Code

The below code will print the even numbers only

int i = 0; void setup() { Serial.begin(9600); } void loop() { if ((i % 2) == 0) { Serial.print("Inside the IF statement, even number: i = "); Serial.println(i); } i++; // increase i by 1 delay(500); }

The result on Serial Monitor:

COM6
Send
Inside the IF statement, even number: i = 0 Inside the IF statement, even number: i = 2 Inside the IF statement, even number: i = 4 Inside the IF statement, even number: i = 6 Inside the IF statement, even number: i = 8 Inside the IF statement, even number: i = 10
Autoscroll Show timestamp
Clear output
9600 baud  
Newline  

※ NOTES AND WARNINGS:

The statements being evaluated inside the parentheses require the use of one or more operators shown below.

Comparison Operators:

x == y (x is equal to y) x != y (x is not equal to y) x < y (x is less than y) x > y (x is greater than y) x <= y (x is less than or equal to y) x >= y (x is greater than or equal to y)

Beware of accidentally using the single equal sign (e.g. if (x = 10) ). The single equal sign is the assignment operator, and sets x to 10 (puts the value 10 into the variable x). Instead use the double equal sign (e.g. if (x == 10) ), which is the comparison operator, and tests whether x is equal to 10 or not. The latter statement is only true if x equals 10, but the former statement will always be true.

This is because C++ evaluates the statement if (x=10) as follows: 10 is assigned to x (remember that the single equal sign is the (assignment operator)), so x now contains 10. Then the 'if' conditional evaluates 10, which always evaluates to TRUE, since any non-zero number evaluates to TRUE. Consequently, if (x = 10) will always evaluate to TRUE, which is not the desired result when using an 'if' statement. Additionally, the variable x will be set to 10, which is also not a desired action.

See Also

※ ARDUINO BUY RECOMMENDATION

Arduino UNO R3
Arduino Starter Kit
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