Running a form with incomplete/empty values - php

Question

I'm writing a script that calculates the total distance, in miles, traveled on a trip. It needs to calculate the total distance, and the distance between any midpoints. Right now it calculates the total distance fine. I am using drop-boxes, and have allowed to it accept up to 5 midpoints. Now, I may just be trying to make this more complicated than it needs to be but...
I'd like to be able to run the script even if three of the midpoint forms are left empty (which would just say "Select City" with a value of " " or null). Is there a way I can have the script run when the three fields of the form are left empty??
EDIT: Each 'index' or 'pont' is defined with a = " ";. I'm using a multidimentional array for the whole script and the 7 drop boxes start with a selected value of "Select City" which has an empty/null value. I just want to know how to run the form/script when two of the mid-point values/drop boxes are left with the initial value of "Select City".
Sorry, here is some of my code:
<?php
if (isset($_POST['Submit'])) {
$StartIndex = stripslashes($_POST['Start']);
$EndIndex = stripslashes($_POST['End']);
if (isset($Distances[$StartIndex][$EndIndex]))
echo "Total trip distance from $StartIndex to $EndIndex is". $Distances[$StartIndex][$EndIndex]." miles<br/>";
else
echo "Distance could not be calculated";
}
?>
This is where I'm stopped at...
<?php
if (isset($_POST['Submit'])) {
$Point1 = stripslashes($_POST['1']);
?>
^^the other four midpoints are the same, I have zero clue how to still run the form when only the start city, end city, and two mid-point cities are selected. I'd add the whole script but it very long with the multidimensional array
To see what my form looks like you can go to >> 131.118.95.215/users/mjswiontek0/project/city/citytocity.php

Answer 1

Just evaluate your test (e.g. empty($_POST["1"])) on every midpoint to find, if you want to include it into calculation.
See commented (very generic) example:
if (isset($_POST['Submit']))
{
// start with the start index
$PrevIndex = stripslashes($_POST['Start']);
$Point = 1;
$Distance = 0;
do
{
// do we have the N-th midpoint?
$HavePoint = !empty($_POST[$Point]);
// if not, use end point
$NextIndex = stripslashes($_POST[$HavePoint ? $Point : 'End']);
// add distance between the two midpoint to total
$Distance += $Distances[$PrevIndex][$NextIndex];
// make current point the previous point to the next iteration
$PrevIndex = $NextIndex;
// move to the next point for the next iteration
$Point++;
}
while ($HavePoint);
}