Page 181 - Beginning PHP 5.3

Chapter 7: Functions
If a function returns a value, you can assign the value to a variable:

$returnVal = functionName( argument );

You can also pass the return value directly to another function, such as print() :

print( functionName( argument ) );

In general terms, the return value of a function call is an expression, which means you can use a
function ’ s return value anywhere that you can use an expression.

When you call a function from within your script, the PHP engine jumps to the start of that function and
begins running the code inside it. When the function is finished, the engine jumps back to the point just
after the code that called the function and carries on from there. Here ’ s a simple example that illustrates
this point:

< !DOCTYPE html PUBLIC “-//W3C//DTD XHTML 1.0 Strict//EN”
“http://www.w3.org/TR/xhtml1/DTD/xhtml1-strict.dtd” >
< html xmlns=”http://www.w3.org/1999/xhtml” xml:lang=”en” lang=”en” >
< head >
< title > Square roots < /title >
< link rel=”stylesheet” type=”text/css” href=”common.css” / >
< /head >
< body >
< h1 > Square roots < /h1 >
< ?php

echo “The square root of 9 is: “ . sqrt( 9 ) . “. < br/ > ”;
echo “All done! < br/ > ”;
? >
< /body >
< /html >
This code produces the output shown in Figure 7 - 1 . Here ’ s how it works:

❑ After displaying the XHTML page header, the first echo() line is run, and the PHP engine
evaluates the expression after the echo() statement. This includes a function call to PHP ’ s built -
in sqrt() function, which determines the square root of its argument (in this case, 9 )
❑ The engine jumps to the code for the sqrt() function and runs it. The function does its job and
exits, returning the value 3
❑ The engine jumps back to the first echo() statement and, now that it knows the result of the call
to sqrt() , evaluates the rest of the expression, producing the string: “ The square root of 9
This string value is then displayed in the Web page using the echo() statement
is: 3. ”
❑ Finally, the engine moves to the next line of code, and displays the “ All done! ” message

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