每日一题（7）

Maybe the serial articles should be called "two questions every two days"

--by author

11. Consider the following segment of code:

<?php

define("STOP_AT", 1024);

$result = array();

/* Missing code */

{

$result[] = $idx;

}

print_r($result);

?>

What should go in the marked segment to produce the following array output?

Array

{

[0] => 1

[1] => 2

[2] => 4

[3] => 8

[4] => 16

[5] => 32

[6] => 64

[7] => 128

[8] => 256

[9] => 512

}

A. foreach($result as $key => $val)

B. while($idx *= 2)

C. for($idx = 1; $idx < STOP_AT; $idx *= 2)

D. for($idx *= 2; STOP_AT >= $idx; $idx = 0)

E. while($idx < STOP_AT) do $idx *= 2

Answer:

 As it is only possible to add a single line of code to the segment provided, the only statement that makes sense is a for loop, making the choice either C or D. In order to select the for loop that actually produces the correct result, we must first of all revisit its structural elements. In PHP, for loops are declared as follows:

for (<init statement>; <continue until statement>; <iteration statement>)

where the <init statement> is executed prior to entering the loop. The for loop then begins executing the code within its code block until the <continue until> statement evaluates to False. Every time an iteration of the loop is completed, the <iteration statement> is executed.

Applying this to our code segment, the correct for statement is:

for ($idx = 1; $idx < STOP_AT; $idx *= 2) or answer C.

12. Choose the appropriate function declaration for the user-defined function is_leap(). Assume that, if not otherwise defined, the is_leap function uses the year 2000 as a default value:

<?php

/* Function declaration here */

{

$is_leap = (!($year %4) && (($year % 100) || !($year % 400)));

return $is_leap;

}

var_dump(is_leap(1987)); /* Displays false */

var_dump(is_leap()); /* Displays true */

?>

A. function is_leap($year = 2000)

B. is_leap($year default 2000)

C. function is_leap($year default 2000)

D. function is_leap($year)

E. function is_leap(2000 = $year)

Answer:

12. Of the five options, only two are valid PHP function declarations (A and D). Of these two declarations, only one will provide a default parameter if none is passed—Answer A.