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en:reference:language:if [2017/04/07 10:03] (current)
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 +=====if (conditional) and ==, !=, <, > (comparison operators)=====
 +
 +if, which is used in conjunction with a comparison operator, tests whether a certain condition has been reached, such as an input being above a certain number. The format for an if test is:
 +
 +<code cpp>
 +if (someVariable > 50)
 +{
 +  // do something here
 +}
 +</​code>​
 +
 +The program tests to see if someVariable is greater than 50. If it is, the program takes a particular action. Put another way, if the statement in parentheses is true, the statements inside the brackets are run. If not, the program skips over the code.
 +The brackets may be omitted after an if statement. If this is done, the next line (defined by the semicolon) becomes the only conditional statement.
 +
 +<code cpp>
 +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
 +</​code>​
 +
 +The statements being evaluated inside the parentheses require the use of one or more operators:
 +
 +=== Comparison Operators: ===
 +
 +<​code>​
 + 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)
 +</​code>​
 +
 +=== Warning: ===
 +
 +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.
 +
 +if can also be part of a branching control structure using the [[reference:​language:​else|if...else]] construction.
 +
  
en/reference/language/if.txt · Last modified: 2017/04/07 10:03 (external edit)