Oracle Database Tips by Donald Burleson

The commands in PHP language are of the usual variety found in the most modern languages since the advent of C.  The    principal commands of interest in this chapter are if, for, while, for each and switch. These commands are the same in almost all modern programming languages such as C/C++, Java, Perl and PHP.

Conditional Statements

If Statement

The if statement has very simple syntax noted as follows:

if (<expression 1>) { statement block 1; }
elseif (<expression 2>)  { statement block 2; }
else { statement block 3; }

If expression 1 is TRUE, statement block 1 is executed. If it is not TRUE, expression 2 is evaluated, and if TRUE, statement block 2 is executed.  If neither is TRUE, statement block 3 is executed. Only the if part is mandatory, the elseif and else parts can be skipped. The following are examples of perfectly valid if statements:

if ($a == $b) { print "Variable a is equal to variable b"; }

if ($a != 3 } { print "Value of a != 3"; }
else {  print "Value of a is 3"; }

if ($a<0) { $ABS = -$a; }
elseif ($a>0) { $ABS= $a; }
else { $ABS=0; }

Enveloped in a UNIX style script, the last example looks like the following:

    #!/usr/local/bin/php
    <?php
    $a=-1;
    if ($a<0) { $ABS = -$a; }
    elseif ($a>0) { $ABS= $a; }
    else { $ABS=0; }
    print "ABS=$ABS\n";
    ?>

It can be executed like any other shell or Perl script:

    $ ./example2.php
    ABS=1

On UNIX and Linux, the "#!" characters at the very beginning of the file means the full path of the interpreter is used to execute the script. The rest of the script is passed to the interpreter as the command input. Of course, in order to be able to execute the script, script must be given the right to execute like this:

chmod 755 ./example2.php

In the example below, the interpreter is /usr/local/bin/php, and it processes the rest of the script and correctly prints the message ABS=1 at the command prompt. If the given if statement is embedded in a HTML file instead of a script, the following syntax can be used:

    <?php if ($a > 0): ?>
The value of "a" is greater then zero.
<?php endif; ?>

PHP can be embedded in a HTML document and can be used for conditional displaying of HTML elements. The form above is actually quite useful and is definitely preferred over this one:

 if ($a>0) {
   print "<pre>The value of \"a\" is greater then zero.</pre>";
}

Printing HTML tags from PHP using print or echo is considered a bad programming style and should be avoided.

Switch Statement

The switch statement is otherwise known as the multiple choice statement and is logically equivalent, but shorter and more elegant to write, to the if/elseif/else statement with multiple elseif parts. The following is the syntax for the switch statement:

switch ($i) {
case 1:
   echo "Thumb";
   break;
case 2:
   echo "Index finger";
   break;
case 3:
   echo "Middle finger";
   break;
case 4:
   echo "Ring finger";
   break;
case 5:
   echo "Little finger";
   break;
default:
   echo "Greetings, Earthlings!";
   echo "I am from the planet Aldebaran."
   echo "Take me to your leader.";
}

Without the break statement, the switch statement does not finish after reaching one case, but proceeds to the next one. Breaks are necessary and will be explained later.

The following is an alternative example of a switch statement that does not have breaks after each case:

switch ($i) {
case 1:
case 2:
case 3:
case 4: 

case 5:
   echo "I'm human";
   break;
default:
   echo "Greetings, Earthlings!";
   echo "I am from the planet Aldebaran."
   echo "Take me to your leader.";
}

The second switch statement's meaning is, if the number $i is equal to 1,2,3,4 or 5, the statement outputs "I'm human" and outputs the greeting to the Earthlings otherwise. 

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