en:reference:language:if

This shows you the differences between two versions of the page.

— |
en:reference:language:if [2017/04/07 10:03] (current) |
||
---|---|---|---|

Line 1: | Line 1: | ||

+ | =====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)