Test for equality

A test for equality in computer programming is one of the trickiest tests used to control a computer program. The usual syntax is something like:

IF (test) THEN
 ... do something
ELSE
 ... do something else
END IF

or in the curly brace languages like Java, C (etc.) or PHP:

if (test) {
 ... do something
}
else {
 ... do something else
}

The tricky part is the test syntax. You can simply write x > 4 with no problem (see test for inequality), but if you check for x = 4 you could have a disastrous side effect.

The curly brace languages all require a double equal sign to be used for tests. This may look strange to the beginner, but it distinguishes an assignment from a test. If you use a single equal sign your code may still compile and run, but your results will probably be incorrect.