Real world applications are usually much larger than the examples above. In has been proven that the best way to develop and maintain a large program is to construct it from smaller pieces (functions) each of which is more manageable than the original program.

A function may be defined using syntax such as the following:

Using Default Parameters

When calling a function you usually provide the same number of argument as in the declaration. Like in the function above you usually call it like this :

$result = addition(5, 10);

But you can actually call a function without providing all the arguments by using default parameters.

Function repeat() have two arguments $text and $num. The $num argument has a default value of 10. The first call to repeat() will print the text 15 times because the value of $num will be 15. But in the second call to repeat() the second parameter is omitted so repeat() will use the default $num value of 10 and so the text is printed ten times.

Returning Values

Applications are usually a sequence of functions. The result from one function is then passed to another function for processing and so on. Returning a value from a function is done by using the return statement.

You can return any type from a function. An integer, double, array, object, resource, etc.

Notice that in buildRows() I use the built in function implode(). It joins all elements of $array with the string '</td></tr><tr><td>' between each element. I also use the '.' (dot) operator to concat the strings.

You can also write buildRows() function like this.

Of course it is more convenient if you just use implode().

Real world applications are usually much larger than the examples above. In has been proven that the best way to develop and maintain a large program is to construct it from smaller pieces (functions) each of which is more manageable than the original program.

A function may be defined using syntax such as the following:

Using Default Parameters

When calling a function you usually provide the same number of argument as in the declaration. Like in the function above you usually call it like this :

$result = addition(5, 10);

But you can actually call a function without providing all the arguments by using default parameters.

Function repeat() have two arguments $text and $num. The $num argument has a default value of 10. The first call to repeat() will print the text 15 times because the value of $num will be 15. But in the second call to repeat() the second parameter is omitted so repeat() will use the default $num value of 10 and so the text is printed ten times.

Returning Values

Applications are usually a sequence of functions. The result from one function is then passed to another function for processing and so on. Returning a value from a function is done by using the return statement.

You can return any type from a function. An integer, double, array, object, resource, etc.

Notice that in buildRows() I use the built in function implode(). It joins all elements of $array with the string '</td></tr><tr><td>' between each element. I also use the '.' (dot) operator to concat the strings.

You can also write buildRows() function like this.

Of course it is more convenient if you just use implode().dasf

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.

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.

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.

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.

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

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.