Control Structure
The next examples will show you how to use control structures in PHP. I won't go through all just the ones that i will use in the code examples in this site. The control structures are
if
else
while
for
If Else
The if statement evaluates the truth value of it's argument. If the argument evaluate as TRUE the code following the if statement will be executed. And if the argument evaluate as FALSE and there is an else statement then the code following the else statement will be executed.
Example : visitor- info.php
Source code : visitor-info.phps
The strpos() function returns the numeric position of the first occurrence of it's second argument ('Opera') in the first argument ($agent). If the string 'Opera' is found inside $agent, the function returns the position of the string. Otherwise, it returns FALSE.
When you're using Internet Explorer 6.0 on Windows XP the value of $_SERVER['HTTP_USER_AGENT'] would be something like:
Mozilla/4.0 (compatible; MSIE 6.0; Windows NT 5.1)
and if you're using Opera the value the value may look like this :
Mozilla/4.0 (compatible; MSIE 6.0; MSIE 5.5; Windows NT 5.1) Opera 7.0 [en]
So if i you use Opera the strpos() function will return value would be 61. Since 61 !== false then the first if statement will be evaluated as true and the value of $agent will be set to the string 'Opera'.
Note that I use the !== to specify inequality instead of != The reason for this is because if the string is found in position 0 then the zero will be treated as FALSE, which is not the behaviour that I want.
While Loop
The while() statement is used to execute a piece of code repeatedly as long as the while expresssion evaluates as true. For example the code below will print the number one to nine.
Example : while.php
Source code : while.phps
';
$number += 1;
}
?>
You see that I make the code $number += 1; as bold. I did it simply to remind that even an experienced programmer can sometime forget that a loop will happily continue to run forever as long as the loop expression ( in this case $number < 10 ) evaluates as true. So when you're creating a loop please make sure you already put the code to make sure the loop will end in timely manner. Break The break statement is used to stop the execution of a loop. As an example the while loop below will stop when $number equals to 6. Example : break.php Source code : break.phps ';
if ($number == 6)
{
break;
}
$number += 1;
}
?>
You can stop the loop using the break statement. The break statement however will only stop the loop where it is declared. So if you have a cascading while loop and you put a break statement in the inner loop then only the inner loop execution that will be stopped.
Example : break2.php
Source code : break2.phps
";
if ($room == 2)
{
break;
}
$room += 1;
}
$floor += 1;
echo "
";
}
?>
If you run the example you will see that the outer loop, while ($floor <= 5), is executed five times and the inner loop only executed two times for each execution of the outer loop. This proof that the break statement only stop the execution of the inner loop where it's declared. For The for loop syntax in PHP is similar to C. For example to print 1 to 10 the for loop is like this }
?>
A more interesting function is to print this number in a table with alternating colors. Here is the code
Example : alternate-colors.php
Source : alternate-colors.phps
| Alternating row colors |
This code display different row colors depending on the value of $i. If $i is not divisible by two it prints yellow otherwise it prints gray colored rows.
.JPG)
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