Abscissa and Ordinate Exercise

Inside the directory you created for this course on PHP, create a new folder called Exercise-12-Abscissa-and-Ordinate and put the .php solution files for this exercise within it.

To solve this exercise, we just need to know two things: how to find a given substring inside a string and how to slice a string in PHP. If we know both of these, we're good to go!

Step one is to set up an input prompt and receive the co-ordinate from the user, as stated in the exercise's description. We'll call this input value $point.

Let's get done with this first:

<?php

echo 'Enter the co-ordinate: ';
$point = rtrim(fgets(STDIN));

Step two is to find the index of the comma (,) in $point. This is required so that we could slice $point in two halves at this position and then extract out the abscissa and ordinate from each respective half.

We'll use the strpos() string function to find the index of the comma in $point.

<?php

echo 'Enter the co-ordinate: ';
$point = rtrim(fgets(STDIN));

$index = strpos($point, ',');

Once the index of the comma is found, the next step is compute the abscissa.

The abscissa starts right after the first parenthesis (() in the string $point and ends just before the comma (,). So to extract it, we ought to slice $point from index 1 upto the point where the comma exists (but obviously excluding the comma).

For the slicing, we'll use the string function substr(), keeping in mind that the third argument of substr() takes the length of the slice, NOT its ending position, and that's why we'll have to perform some quick arithmetic to get the correct value for this argument.

Here's the code to do so:

<?php

echo 'Enter the co-ordinate: ';
$point = rtrim(fgets(STDIN));

$index = strpos($point, ',');
$abscissa = substr($point, 1, $index - 1);

Next up, we move to extract the ordinate.

The ordinate begins right after the comma (,) and ends just before the ending parenthesis ()). Likewise, it could be extracted as follows:

<?php

echo 'Enter the co-ordinate: ';
$point = rtrim(fgets(STDIN));

$index = strpos($point, ',');
$abscissa = substr($point, 1, $index - 1);
$ordinate = substr($point, $index + 1, -1);

With the abscissa and ordinate in hand, we make the desired output keeping in mind that we have to leave a blank line before doing so.

Altogether, we get the following code:

<?php

echo 'Enter the co-ordinate: ';
$point = rtrim(fgets(STDIN));

$index = strpos($point, ',');
$abscissa = substr($point, 1, $index - 1);
$ordinate = substr($point, $index + 1, -1);

echo "\n";
echo 'Abscissa: ', $abscissa, "\n";
echo 'Ordinate: ', $ordinate;

And this completes the exercise.