I am doing a bubble sort function and encounter a variable operator problem. There is a switch block at the beginning to determine whether it should be sorted in ascending or descending order. The $operator is intended to be used in the following if condition.
<?php
//bubble sort in ascending/descending order
function bubbleSort($arr, $operation="ascending"){
switch ($operation){
case "ascending":
$operator = ">";
break;
case "descending":
$operator = "<";
break;
}
//each loop put the largest number to the top
for ($i=0; $i<count($arr)-1; $i++){
//compare adjacent numbers
for ($j=0; $j<count($arr)-1-$i; $j++){
//exchange the adjacent numbers that are arranged in undesired order
if ($arr[$j]>$arr[$j+1]){
$temp = $arr[$j];
$arr[$j] = $arr[$j+1];
$arr[$j+1] = $temp;
}
}
}
return $arr;
}
$arr1 = array(1000,10,2,20,-1,-6,-8,0,101);
$arr1 = bubbleSort($arr1, "ascending");
print_r($arr1);
?>
While technically it is possible to put the operator (<
or >
) in a string and compile an expression out of it (using eval()
), most of the time you neither need nor want this. Simply assigning a boolean that decides whether to sort ascending, and then evaluating that boolean is a more common way to go.
Your code then comes down to something like this:
function bubbleSort($arr, $operation="ascending"){
$ascending = ($operation == "ascending");
//each loop put the largest number to the top
for ($i=0; $i<count($arr)-1; $i++){
//compare adjacent numbers
for ($j=0; $j<count($arr)-1-$i; $j++){
//exchange the adjacent numbers that are arranged in undesired order
if (($ascending && ($arr[$j] > $arr[$j+1]))
|| (!$ascending && ($arr[$j] < $arr[$j+1])))
{
$temp = $arr[$j];
$arr[$j] = $arr[$j+1];
$arr[$j+1] = $temp;
}
}
}
return $arr;
}
Of course you can skip the string evaluation and change the $operation="ascending"
parameter to $ascending = true
, leaving out the first line in the function.