PDO INSERT statement not working inside counter loop - php

Question

Can anyone let me know why this PDO Statement won't work inside the for loop? I'm trying to add one to the position for each new entry into the database. for some reason this is breaking. Any ideas on why?
Edit
Please ignore the next position, etc. For other reasons the gp_position can not be AUTO_INCREMENT and next position won't always start at 1. Please focus on why this PDO Statement won't work inside the loop.
$nextPosition = 1;
$imgID = 1;
$indb_gridID = 1;
$timesToRepeat = 33;
$indb_mem_id = ($this->user->is_logged_in()) ? $this->user->info['id'] : 1;
for($i=1; $i<=$timesToRepeat; $i++) {
// now add the image to the grid positions
$stmt = dbpdo::$conn->prepare("INSERT INTO grid_positions SET
gp_mem_id = :memID,
gp_g_id = :gridID,
gp_img_id = :imgID,
gp_position = :position");
$stmt->bindParam(':memID', $indb_mem_id, PDO::PARAM_INT);
$stmt->bindParam(':gridID', $indb_gridID, PDO::PARAM_INT);
$stmt->bindParam(':imgID', $imgID, PDO::PARAM_INT);
$stmt->bindParam(':position', $nextPosition, PDO::PARAM_INT);
$stmt->execute();
$nextPosition++;
}

Answer 1

Try this refactored code:
$nextPosition = 1;
$imgID = 1;
$indb_gridID = 1;
$timesToRepeat = 33;
$indb_mem_id = ($this->user->is_logged_in()) ? $this->user->info['id'] : 1;
// prepare the statement once:
$stmt = dbpdo::$conn->prepare("INSERT INTO grid_positions SET
gp_mem_id = :memID,
gp_g_id = :gridID,
gp_img_id = :imgID,
gp_position = :position");
$stmt->bindParam(':memID', $indb_mem_id, PDO::PARAM_INT);
$stmt->bindParam(':gridID', $indb_gridID, PDO::PARAM_INT);
$stmt->bindParam(':imgID', $imgID, PDO::PARAM_INT);
$stmt->bindParam(':position', $nextPosition, PDO::PARAM_INT);
for($i=1; $i<=$timesToRepeat; $i++) {
// exec statement with current values:
$stmt->execute();
$nextPosition++;
}