Increasing array elements while in foreach loop in php? [duplicate] - php

Question

This question already has answers here:
How does PHP 'foreach' actually work?
(7 answers)
Closed 8 years ago.
Consider the code below:
<?php
$arr = array();
$arr['b'] = 'book';
foreach($arr as $key=>$val) {
print "key=>$key\n";
if(!isset($arr['a']))
$arr['a'] = 'apple';
}
?>
It is not displaying 'a'. How foreach works with hash-table(array), to traverse each element. If lists are implement why can't I add more at run time ?
Please don't tell me that I could do this task with numeric based index with help of counting.

Answer 1

Foreach copies structure of array before looping(read more), so you cannot change structure of array and wait for new elements inside loop. You could use while instead of foreach.
$arr = array();
$arr['b'] = 'book';
reset($arr);
while ($val = current($arr))
{
print "key=".key($arr).PHP_EOL;
if (!isset($arr['a']))
$arr['a'] = 'apple';
next($arr);
}
Or use ArrayIterator with foreach, because ArrayIterator is not an array.
$arr = array();
$arr['b'] = 'book';
$array_iterator = new ArrayIterator($arr);
foreach($array_iterator as $key=>$val) {
print "key=>$key\n";
if(!isset($array_iterator['a']))
$array_iterator['a'] = 'apple';
}

Answer 2

I think you need to store array element continue sly
Try
<?php
$arr = array();
$arr['b'] = 'book';
foreach($arr as $key=>$val) {
print "key=>$key\n";
if(!isset($arr['a']))
$arr['a'][] = 'apple';
}
print_r($arr);
?>

Answer 3

In order to be able to directly modify array elements within the loop precede $value with &. In that case the value will be assigned by reference.
http://cz2.php.net/manual/en/control-structures.foreach.php

Answer 4

Try this:
You will get values.
<?php
$arr = array();
$arr['b'] = 'book';
foreach($arr as $key=>$val) {
print "key=>$key\n";
if(!isset($arr['a']))
$arr['a'] = 'apple';
}
echo '<pre>';
print_r($arr);
?>
Output:
key=>b
<pre>Array
(
[b] => book
[a] => apple
)

Answer 5

If you want to check key exist or not in array use array_key_exists function
Eg:
<?php
$arr = array();
$arr['b'] = 'book';
print_r($arr); // prints Array ( [b] => book )
if(!array_key_exists("a",$arr))
$arr['a'] = 'apple';
print_r($arr); // prints Array ( [b] => book [a] => apple )
?>
If you want to use isset condition try like this:
$arr = array();
$arr['b'] = 'book';
$flag = 0;
foreach($arr as $key=>$val) {
print "key=>$key\n";
if(!isset($arr["a"]))
{
$flag = 1;
}
}
if(flag)
{
$arr['a'] = 'apple';
}
print_r($arr);

Answer 6

How about using for and realtime array_keys()?
<?php
$arr = array();
$arr['b'] = 'book';
for ($x=0;$x<count($arr); $x++) {
$keys = array_keys($arr);
$key = $keys[$x];
print "key=>$key\n";
if(!isset($arr['a']))
$arr['a'] = 'apple';
}