PHP strpos dont works properly(Path Generator) - php

Question

I wanted to create a function that generates an image path from an array.The function has one argument and that argument is for you to decide from which folder you want to choose images.
So I have 90 elements in an array and each element is a path.Now I don't want a .png image so I wanted to create something like this(but it didn't work for me):
public function getRandomPath($RoboticOrArenag)
{
if ($RoboticOrArenag == 'Robotic' || $RoboticOrArenag == 'robotic') {
$countofarray = count($this->allImagesRobotic);
} else if ($RoboticOrArenag == 'Arenag' || $RoboticOrArenag == 'arenag') {
$countofarray = count($this->allImagesArenag);
} else {
$RoboticOrArenag = 0;
}
$randomNumber = rand(0, $countofarray);
if ($RoboticOrArenag == 'Robotic' || $RoboticOrArenag == 'robotic') {
if($randomNumber==50){
$randomNumber--;
}
else if ($randomNumber==0){
$randomNumber++;
}
$randomNumberPath = $this->allImagesRobotic[$randomNumber];
} else if ($RoboticOrArenag == 'Arenag' || $RoboticOrArenag == 'arenag') {
if($randomNumber==33){
$randomNumber--;
}
else if ($randomNumber==0){
$randomNumber++;
}
$randomNumberPath = $this->allImagesArenag[$randomNumber];
while(strpos($randomNumberPath, '.png') == true){
$randomNumber = rand(0, $countofarray);
$randomNumberPath = $this->allImagesArenag[$randomNumber];
}
} else {
$randomNumberPath = 0;
}
$randomPath = "/img/$RoboticOrArenag/$randomNumberPath";
return $randomPath;
}