Function call to set variable doesn't work - php

Question

the following code is modified after suggestion does get the $i $j works well
<?php
$i=1;
$j=1;
function fixIndex() {
global $i, $j;
$a=$j-$i;
if ($a === 60){
$i += 60;
}
$j++;
}
but it does not work on my main code as follow:
$times = array();
$values1 = array();
$values2 = array();
$values3 = array();
$values4 = array();
$i=1;
$j=1;
$file_lines = file($DispFile, FILE_IGNORE_NEW_LINES|FILE_SKIP_EMPTY_LINES);
foreach( $file_lines as $line_num => $line_value) {
fixIndex();
if ($line_num < $i)continue; // skip records in 60* range
$line_elements = explode(",", $line_value);
$times[] = date("H:i:s", $line_elements[0]);
$values1[] = $line_elements[1];
$values2[] = $line_elements[2];
$values3[] = $line_elements[3];
$values4[] = $line_elements[4];
}
After the foreach loop I call for the fixIndex(), trying to get the $i value for the next line of code(if ($line_num < $i)continue;) to skip 60 records before i build an array. That $i doesn't seem to skip the record. If I change that $i to a number on it ($line_num < 60 )continue; Than it does skip the 60 records.
also is there any change of the program flow if this php program do a refresh on the every 10 sec on the web, What I mean is did $i and $j rest to 1 every time after refresh?
Thanks again to anyone for any help

Answer 1

You can use pass by reference to avoid needing global variables here. What that means is the function will modify the variables that were passed to it.
https://secure.php.net/manual/en/language.references.pass.php
<?php
function fixIndex(&$i, &$j) {
global $i, $j;
if ($j - $i == 5) {
$i += 5;
}
$j++;
}
$i=1;
$j=1;
for ($k=0;$k<=20; $k++){
fixIndex($i, $j);
echo $i.'<br />';
echo $j.'<br />';
}
?>
Also, I changed "$i + 5" (which doesn't make anything happen) to "$i += 5" so that it modifies the variable $i.

Answer 2

You are not storing your incremented value of $i.
<?php
$i=1;
$j=1;
function fixIndex() {
global $i, $j;
if ($j - $i == 5){
$i = $i+5;
}
$j++;
}
for ($k=0;$k<=20; $k++){
fixIndex();
echo $i.'<br />';
echo $j.'<br />';
}
Demo : https://eval.in/518511

Answer 3

You probably could describe what you want to do like this:"increment $i by 5 every time $j has grown by 5".This could be implemented in a straight and very compact form like this.(The solution covers all cases, and is not depending on the upper limit of the iteration.)
<?php
function fixIndex(&$i,$j) {
if ( ($j>1) && (($j-1) % 5 == 0) ) $i += 5;
}
$i = 1;
for ($j=1;$j<=20; $j++){
fixIndex($i,$j);
echo "\$j=$j, \$i=$i <br />";
}
Notes:
( ($j-1) % 5 == 0 )
…means: when $j -1 can be devided by 5 without a remainder (% 5 = "modulo 5").
function fixIndex(&$i,$j)
&$i means that a reference (pointer) to the memory of the $i variable is accepted instead of its value. This is necessary since the function is modifying the value of $i. So, you would not need the global statement.On the other hand the $j variable is not modified and thus can be accepted as a value.
Result:
$j=1, $i=1
$j=2, $i=1
$j=3, $i=1
$j=4, $i=1
$j=5, $i=1
$j=6, $i=6
$j=7, $i=6
$j=8, $i=6
$j=9, $i=6
$j=10, $i=6
$j=11, $i=11
$j=12, $i=11
$j=13, $i=11
$j=14, $i=11
$j=15, $i=11
$j=16, $i=16
$j=17, $i=16
$j=18, $i=16
$j=19, $i=16
$j=20, $i=16