array in php function undefined - php

Question

For training purposes i need to make a function which tells me the 'travel cost' between 2 cities. The book tells me to type this function:
<?php
function travelcost($start, $destination)
{
$travelcost = array();
$travelcost[1] = array();
$travelcost[2] = array();
$travelcost[3] = array();
$travelcost[4] = array();
$travelcost[1][1] = 0;
$travelcost[1][2] = 30;
$travelcost[1][3] = 60;
$travelcost[1][4] = 90;
echo($travelcost[$start][$destination] . " Euro's");
}
?>
In addition i've created this form to ask for a start and a destination:
<form action="<?php echo $_SERVER['PHP_SELF']; ?>" method="post">
Start: <select name="start" value="true">
<option value="start[]">Amsterdam</option>
<option value="start[]">Utrecht</option>
<option value="start[]">Den Haag</option>
<option value="start[]">Rotterdam</option>
</select>
Destination: <select name="destination" value="true">
<option value="destination[]">Amsterdam</option>
<option value="destination[]">Utrecht</option>
<option value="destination[]">Den Haag</option>
<option value="destination[]">Rotterdam</option>
</select>
<p><input type="submit" name="calculate" value="Calculate"</p>
</form>
Followed by:
<?php
if(isset($_POST["start"])&& isset($_POST["destination"]))
{
travelcost($_POST['start'], $_POST['destination']);
}
?>
This gives me Undefined index: start[]
I know im doing it wrong, but i just can't see the logic in the function and the array. I assume the function is correct because it's right out of the book but i'm also not sure about that.
Can someone help me out?

Answer 1

This is wrong,
<option value="start[]">Amsterdam</option>
^ ^
It should be
<option value="start">Amsterdam</option>
or
<option value="Amsterdam">Amsterdam</option>
Same for all options in start and destination.
According to your function `travelcost(), your select should be
Start: <select name="start" value="true">
<option value="1">Amsterdam</option>
<option value="1">Utrecht</option>
<option value="1">Den Haag</option>
<option value="1">Rotterdam</option>
</select>
Destination: <select name="destination" value="true">
<option value="1">Amsterdam</option>
<option value="2">Utrecht</option>
<option value="3">Den Haag</option>
<option value="4">Rotterdam</option>
</select>