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PHP Tutorial
Part 3 - IF
Statements
Introduction
Over
the past two parts I have shown you the basics of text
in PHP and how to store it as variables. In this part of
the tutorial I will show you how to use IF statements to
make decisions in your scripts.
The Basics Of
IF
If statements are used to
compare two values and carry out different actions based
on the results of the test. If statements take the form
IF, THEN, ELSE. Basically the IF part checks for a
condition. If it is true, the then statement is
executed. If not, the else statement is
executed.
IF
Strucure
The structure of an IF
statement is as follows:
IF (something == something
else)
{
THEN Statement
} else {
ELSE
Statement
}
Variables
The
most common use of an IF statement is to compare a
variable to another piece of text, a number, or another
variable. For example:
if ($username ==
"webmaster")
which would compare the
contents of the variable to the text string. The THEN
section of code will only be executed if the variable is
exactly the same as the contents of the quotation marks
so if the variable contained 'Webmaster' or 'WEBMASTER'
it will be false.
Constructing The THEN
Statment
To add to your script,
you can now add a THEN statement:
if ($username == "webmaster")
{
echo "Please enter your password
below";
}
This will only display this
text if the username is webmaster. If not, nothing will
be displayed. You can actually leave an IF statement
like this, as there is no actual requirement to have an
ELSE part. This is especially useful if you are using
multiple IF statements.
Constructing The ELSE
Statement
Adding The ELSE
statement is as easy as the THEN statement. Just add
some extra code:
if ($username == "webmaster")
{
echo "Please enter your password below";
} else
{
echo "We are sorry but you are not a recognised
user";
}
Of course, you are not limited
to just one line of code. You can add any PHP commands
in between the curly brackets. You can even include
other IF statments (nested statements).
Other
Comparisons
There are other ways
you can use your IF statement to compare values.
Firstly, you can compare two different variables to see
if their values match e.g.
if ($enteredpass ==
$password)
You can also use the standard
comparision symbols to check to see if one variable is
greater than or less than another:
if ($age < "13")
Or
:
if ($date >
$finished)
You can also check for multiple
tests in one IF statement. For instance, if you have a
form and you want to check if any of the fields were
left blank you could use:
if ($name == "" || $email == "" ||
$password == "") {
echo "Please fill in all the
fields";
}
Part 4
In
part four I will show you some other ways of using your
PHP script to do other types of checks and loops.
© 1999 - 2001
David Gowans
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