Intro to PHP: Math Operators
Math Operators are used to perform numeric calculations. It is pretty much just like in grammar school math class.
At the bottom of this page there is a code editor pre-loaded with the lesson's code.
$hrsPlayedMon = 10;
$hrsPlayedTues = 9;
$hrsTotal = $hrsPlayedMon + $hrsPlayedTues;
echo $hrsTotal;
➼ $hrsPlayedMon is a variable that repersents how many hours
Commander Bob played video games on Monday. He played 10 hours.
➼ $hrsPlayedTues is a variable that repersents the number of hours
Commander Bob played video games on Tuesday. He played 9 hours.
➼ $hrsTotal is a variable that repersents that number of hours Commander Bob
played on Monday (10) plus the number of hours he played on Tuesday (9).
He played a total of 19 hours between Monday and Tueday.
➼ echo $hrsTotal; will print the value of $hrsTotal
Output: 19
$hrsDifference = $hrsPlayedMon - $hrsPlayedTues;
echo $hrsDifference;
➼ $hrsDifference is a variable
that repersents the number of hours Comander Bob played on Monday (10)
minus the number of hours he played on Tuesday (9).
➼ echo $hrsDifference; Will print the
value of $hrsDifference
Output: 1
define("NUMBER_WEEK_DAYS", 7);
$weekMultiple = NUMBER_WEEK_DAYS * $hrsPlayedMon;
echo $weekMultiple;
➼ NUMBER_WEEK_DAYS is a
constant that equals 7.
➼ $weekMultiple is a variable
used to predict how many hours Commander Bob will play video games during the week.
It multiplies NUMBER_WEEK_DAYS (7) and $hrsPlayedMonday (10). This
is probably not the best prediction algorithm, but I think it is sufficent for our
example.
➼ echo $weekMultiple; will
print the value of $weekMultiple
Output: 70
$daysCounter = 2;
$avgDailyHours $hrsTotal / $daysCounter
echo $avgDailyHours;
➼ $daysCounter is a
variable that repersents how many days we have been tracking Commander Bob's video
game hours. We have data for Monday and Tuesday, so I set $daysCounter equal
to 2.
➼ $avgDailyHours is a
variable that calculates the average number of hours that Commander Bobby
plays per day. It is equal to $hrsTotal (19) divided by $daysCounter (2).
➼ echo $avgDailyHours;
will print the value of $avgDailyHours
Output: 9.5
An exponent repersents how many times you should multiple the base number by itself.
Example: 34,which in PHP is written 3 ** 4,
equals 3*3*3*3, which equals 81. We say 3 ** 4 as 'three to
the fourth power'. 3 is the base number and 4 is the exponent. If you do
not understand what an exponent is, you might want to visit this page:
Algebra Class: Exponents.
$monSquared = $hrsPlayedMon ** 2;
echo $monSquared;
➼ $monSquared is a
variable that repersents $hrsPlayedMon (10) to the second power. (10 ** 2)
➼ echo $monSquared;
will print the value of $monSquared
Output: 100
Negation
means getting the opposite. The opposite of a possitive number would be negative.
The opposite of a negative number would be possitive. The minus symbol (-) is used to
show negation
Example 1: $a = 3; $b = -$a; => $b = -3
Example 2: $a = -5; $b = -$a; => $b = 5.
$monOpposite = - $hrsPlayedMon;
echo $monOpposite;
➼ $monOpposite is a
variable that repersents the opposite of $hrsPlayedMon.
➼ echo $monOpposite;
will print the value of $monOpposite
Output: -10
Modul will find the remainder of two numbers when they are divided. The
remainder is basically what is left after 2 numbers are divided.
# Example 1: 19 / 3 = 6 1/3, or 6 remainder 1, modul is 1
# Example 2: 11 / 4 = 2 3/4, or 2 remainder 3, modul is 3
(if you don't understand remainders, try visiting Math is fun: Remainders
$daysCounter = 2;
echo $hrsTotal % $daysCounter;
➼ $daysCounter is intialized
at 2.
➼ echo $hrsTotal % $daysCounter;
will print the remainder when $hrsTotal(19)
is divided by $daysCounter (2).
Output: 1
The increment operator adds one to the value of a variable
To give the following example some context, let's say you are writing code for an online browser game.
$currentLevel = 1;
echo 'You completed level: ' . $currentLevel ++;
echo "\n";
echo "You are now on level " . $currentLevel;
➼ $currentLevel represents the current level being played.
Its value is initialized at 1.
At the end of each level you write code to tell the player what level they completed and
then increment (add 1) to the game level:
➼ echo 'You completed level: ' . $currentLevel++; This code will
print 'You completed level: ' followed by the value of $currentLevel. Then it will add
1 to the value of $currentLevel.
Output: You completed level: 1 *Value of $currentLevel after the echo statement: 2
➼echo "\n"; inserts a line break
Now you write code to let the player know what level they are about to start:
➼echo 'You are now on level ' . $currentLevel;
will print 'You are now on level ' followed by the value of $currentLevel.
Output: You are now on level 2
$currentLevel = 1;
echo ++$currentLevel;
echo " " . ++$currentLevel;
➼ $currentLevel = 1; The variable $currentLevel is intialized
back at 1.
➼ echo ++$currentLevel; $currentLevel will be incremented, then printed
Output: 2
➼ echo " " . ++$currentLevel; will print a blank space, increment $currentLevel,
then print the value of $currentLevel
Output: 3
Decrement subtracts one from the value. It works simularly to increment, but subtracts instead of adds.
So, you are still working on that online browser game. You have to write code to keep track of how many lives the player has remaining. Let's look at the difference between pre- and post- decrement.
$livesLeft = 3;
echo $livesLeft-- . " ";
echo $livesLeft-- . " ";
echo $livesLeft-- . " ";
➼ $livesLeft = 3; The player starts with 3 lives.
➼ echo $livesLeft-- . " "; Will print the value of $livesLeft,
then decrement it.
Output: 3
➼ echo $livesLeft-- . " "; Will print the value of $livesLeft,
then decrement it.
Output: 2
➼ echo $livesLeft-- . " "; Will print the value of $livesLeft,
then decrement it.
Output: 1
$livesLeft = 3;
echo --$livesLeft . " ";
echo --$livesLeft . " ";
echo --$livesLeft . " ";
➼ $livesLeft = 3; $livesLeft is intialized back at 3.
➼ echo --$livesLeft . " "; Decrements $livesLeft then prints the value
of $livesLeft Output: 2
➼ echo --$livesLeft . " "; Decrements $livesLeft then prints the value
of $livesLeft Output: 1
➼ echo --$livesLeft . " "; Decrements $livesLeft then prints the value
of $livesLeft Output: 0
Think about how you would want the $livesLeft code to work. Do you think you would pre-decrement or post-decrement?
Background:
Imagine you live in a dark and dreary post-apocalyptic Earth. Earth has been taken over by
aliens. Due to their bug-like apperance, the aliens are nicknamed "bugs". As a commander
in the human resistance, and a web developer, you provide a shining light of hope to
Earth's orginally inhabitant.
Assignment:
You are writing code to keep track of bugs living in your district. Write the following
statements in PHP code:
Example:
There were 20 bugs, then you killed 5
// Initialize Variables
$bugs = 20;
$bugsKilled = 5;
// Number of bugs left
$bugs = $bugs - $bugsKilled;
Statements:
1) There are 10 bugs on the south-side and 15 bugs on the north-side.
2) You and your squad encounter 10 bugs. Each bullet fired killed 1 bug.
7 bullets were fired
3) A ship just landed with 11 bugs. There of your cadets found the landing site.
Each cadet killed 3 bugs. You have to kill the remainder.
4) 100 bugs have arrived on Eath. 10% of them enter your district.
5) Each TNT explosive kills 5 bugs. Two TNT explosives were used on the bugs.
Make sure to play around with your variables and statements in the code editor box below.
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