how to upload image using php function - php

Question

This is my code. I tried to upload an image using this PHP code. $mainCName, $mainCImage save in the database. But, the image does not upload to the uploadedimage folder. Can you help me please?.
public function add_main_category($mainCName, $mainCImage){
$query = "SELECT * FROM mainCategory WHERE mainCName='$mainCName'";
$result = $this->db->query($query) or die($this->db->error);
$count_row = $result->num_rows;
if($count_row == 0){
$imgfile=$_FILES["$mainCImage"];
$extension = substr($imgfile,strlen($imgfile)-4,strlen($imgfile));
$allowed_extensions = array(".jpg",".jpeg",".png",".gif");
if(!in_array($extension,$allowed_extensions))
{
echo "<script>alert('Invalid format. Only jpg / jpeg/ png /gif format allowed');</script>";
}
else{
$imgnewfile=md5($imgfile).$extension;
move_uploaded_file($_FILES["mainCImage"]["tmp_name"],"uploadedimage/".$imgnewfile);
}
$query = "INSERT INTO maincategory(mainCName,mainCImage) VALUES('$mainCName','$mainCImage')";
$result = $this->db->query($query) or die($this->db->error);
return true;
}
else{return false;}
}