Web Programming
PHP flow of control & functions
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Program Control
• To date all program flow has been sequential (in
program line sequence)
• Other control mechanisms are required for more
complex programs:
– Alternative pathways depending on conditional values (if
statements, switch statements)
– Repeated instructions (for loops, while loops)
– Creating program functions which can be defined and used
multiple times
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Alternative pathways
• Conditions can be tested to allow different pathways
of instructions to be followed (if statement)
• For example textbox input values can be checked to
see:
– If any value has been entered (blank?) & if so an entry can
be requested
– If the correct type of value has been entered (numeric?) &
if not a correct value can be requested
– Otherwise (i.e. non-blank, correct type of data) so process
value
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Conditional Test Statement
• if statement
– elseif clause (alternative if)
– else clause (default where no if… else if
true)
• Switch statement
– Used for large number of conditions
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If statement
If a condition is true then some consequence follows
General Format
If (condition) statement;
If (condition) {
statement;
// consequence of a true condition
…………..
}
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If…elseif….else
• Where there series of alternative conditions we need
else if clauses and also a default action if none of the
conditions are true
if (condition is true) then …….
else if (alternative condition is true) then…..
else if (another alternative condition is true) then ….
…………………………………………………
else do this (no condition required)
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If …. ElseIf
General Format
if (condition) {
statement;
}
elseif (condition) {
statement;
}
else statement;
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Condition Checking
• Conditions are placed inside round brackets
• Conditions are either true (causing statements to be
executed and no further alternative conditions are
considered) or false (causing next alternative to be
considered)
• They are often formulated as a variable compared to
a value or other variable, but can be a function which
evaluated to true or false [e.g. is_numeric( variable)
]
• Note particularly that for a condition is equal to is ==
(and NOT just = )
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Comparison Operators
Test
Effect
Operator
==
Equal to
Example
Result
if ($x == 6){
$x = $y + 1;
$y = $x + 1;
}
Run the second and third statements
if the value of $x is equal to 6.
!=
Not equal
to
if ($x != $y) {
$x = 5 + 1;
}
Run the second statement if the
value of $x is not equal to the value
of $y.
<
Less than
if ($x < 100) {
$y = 5;
}
Run the second statement if the
value of $x is less than 100.
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Comparison Operators (2)
Test
Effect
Operator
Example
Result
Run the second statement if the
value of $x is greater than 51.
>
Greater
than
if ($x > 51) {
print "OK";
}
>=
Greater
than or
equal to
if (16 >= $x) {
Run the second statement if 16 is
print "x=$x"; greater than or equal to the value of
}
$x.
<=
Less than if ($x <= $y) {
Run the second and third statements
print "y=$y"; if the value of $x is less than or
or equal to
print "x=$x"; equal to the value of $y.
}
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If example
<?php
$destination= "Mexico";
if ($destination== "Iceland") {
print "Remember to pack a woolly jumper";
}
elseif ($destination== "Mexico") {
print "Remember to pack sun cream";
}
else print "Stay at home"; // default result
?>
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Exercise 1 – to try
• Adapt the previous If example to work out interest
in a savings account
– Assign an initial amount to the account and print it
– If the amount is 0 then
• Print your account is empty
– Else If the amount is at less than 100 (£) then
• Add 1% interest to the amount
• Print the new overall amount
– Else If the amount is at least 100 (£) then
• Add 2% to the amount
• Print the new overall amount
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Using multiple conditions
• When using more than one condition the logical AND & OR is
required
• In PHP AND is && and BOTH conditions must be true
• In PHP OR is II and EITHER condition must be true
• Negation is !
• If x is greater than 10 but less than 20 is expressed as
If ($x > 10 && $x < 20) {
……….
}
• If y is less than 50 or above 100 is expressed as
If ($y < 50 || $y > 100) {
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……….
}
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Switch Statement (multiple if…..
elseif..)
General Format
switch (expression) {
Case "value 1":
statement;
break;
Case "value 2":
statement;
break;
Default:
statement;
}
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Switch example
<?php
$destination = "Mexico";
Switch ($destination) {
case "Mexico":
print "Remember to pack sun cream";
break;
case "Iceland":
print "Remember to pack a woolly jumper";
break;
Default:
Print "Stay at home";
}
?>
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Example – age group survey
• Problem: Design a simple age group survey, using an
HTML form to collect the age and using PHP to return the
following message:
– if the participant is younger than 18 display
"You're young – enjoy it!";
– if the participant is older than 18 and less than 50 display
"You're in the prime of your life";
– If the participant is older than 50 display
"You can retire soon – hurrah!"
– Display other relevant message if you wish
age_front.html
age_back.php
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age_front.html
<html><body>
Age Survey Form<br /><br />
<form action="age_back.php" method="post">
Enter Your Age<input type="text" name="age"><br /><br />
<input type="submit" value="Click To Submit">
</form>
</body></html>
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age_back.php
<?php
print "Thank you for taking the survey!<br /><br />\n";
$Age = $_POST["age"]; // receive posted age from textbox
if ($Age < 18) {
print ("You're young – enjoy it!<br />\n");
} elseif ($Age >= 18 && $Age < 50) {
print "You're in the prime of your life! <br />";
} elseif ($Age >= 50) {
print "You can retire soon – hurrah! <br />";
} else {
print "number not a positive number";
}
?>
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Exercise 2 – to try
if (condition) {
statement;
}
elseif (condition) {
statement;
}
else statement;
Create a php program to check the stock level
- Assume that an HTML page with a form using
method = "post" & a textbox with
name = "stocklevel"
- Receive the posted value the user places in
the textbox
- Where the stock level is below 20 print an
"emergency reorder" statement
- Where the stock level is between 20 & 49
print a "standard reorder" statement
- Otherwise print "stock level is OK"
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Nested if statements
• Using if … elseif… else to check textbox for numbers
$input = $_POST["value"];
if ($input == "") {
print "textbox value is blank – must enter a value";
}
elseif (!is_numeric($input)) {
print "enter a valid number in the textbox";
}
else {
…..[Input OK and can now be processed]
}
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Program Loops
• In order to perform repeated operations efficiently
methods of looping through code instructions (for
loops or while loops) are required
• For loops are used when the number of iterations of
the loops is known in advance
• While loops continue until a condition is met (so the
exact number of iterations is not known in advance)
• Loops can be used for printing out rows of a table,
printing sequences of values, simulating a number of
values (e.g. dice throws, coin flips)
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For Loop
General Format
For (start expression, stop expression, increment expression)
{
[code statements]
}
FOR LOOP is used when you know the exact number of
times a program loop needs to go round whereas a WHILE
LOOP is used when you don’t (you need a condition to
test when the loop needs to finish)
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For Loop example
• <?php
for ($i = 1; $i <= 5; $i = $i + 1) {
print "Number $i <br />\n";
}
?>
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Output:
1
2
3
4
5
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For Loop example explained
for ($i = 1; $i < =5; $i = $i + 1) {
print "Number $i <br />\n";
}
Processing
Output
$i=1 1<=5 is true
print "Number $i" $i = $i (1) + 1 so $i = 2
1
$i=2 2<=5 is true
print "Number $i" $i = $i (2) + 1 so $i = 3
2
$i=3 3<=5 is true
print "Number $i" $i = $i (3) + 1 so $i = 4
3
$i=4 4<=5 is true
print "Number $i" $i = $i (4) + 1 so $i = 5
4
$i=5 5<=5 is true
print "Number $i" $i = $i (5) + 1 so $i = 5
5
$i=6 6<=5 is not true END
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Exercise 3 – to try
• A. Create a program to print out all the odd numbers
from 1 to 21 using a for loop
• B. Create a program to print out all the numbers
from 10 to 1 using a for loop
• C. Create a program to print the numbers from 1 to 5
with the square of each number (using a for loop)
- (e.g. square of 1 is 1* 1 or 1, 2 is 2*2 or 4 etc)
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While Loop
• While statement
while (condition is true) {
do code
}
• eg.
<?php
while(there are still rows to read from a
database)
{
read in row; move to the next to row;
}
?>
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While loop example
• <?php
$x = 1;
// initial value of loop variable
while ($x <=3) {
// while end check condition
print "number is $x<br>";
$x = $x + 1;
// increment of loop variable
}
?>
Output:
number is 1
number is 2
number is 3
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While loop example explained
$x = 1;
while ($x < =3) {
print "number is $x<br>";
$x = $x + 1;
}
Processing
Output
$x = 1 1<=3 is true
print "number is $x" $x=$x (1) + 1 so $x=2
1
$x = 2 2<=3 is true
print "number is $x" $x=$x (2) + 1 so $x=3
2
$x = 3 3<=3 is true
print "number is $x" $x=$x (3) + 1 so $x=4
3
$x = 4 4<=3 is not true END
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Exercise 4 – to try
• Repeat exercise 3 using while loops instead of
for loops
• A. Create a program to print out all the odd
numbers from 1 to 21
• B. Create a program to print out all the
numbers from 10 to 1
• C. Create a program to print the numbers from
1 to 5 with the square of each number
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Do while loop example
• <?php
$x = 1;
do
{
$x = $x + 1;
print "number is $x<br>";
}
while ($x < =3);
?>
Output:
number is 2
number is 3
number is 4
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Counting the number of loops
• Counting - how many times a loop has gone round
– Initialise a count variable before the loop
– Increment the variable inside the loop
– Print the final number after the loop has finished
e.g. $count = 0; // initialise as 0
for ($i = 0; $i<10; $i=$i+1){
$count = $count + 1; // increment by 1
}
print $count; // prints final count value - 10
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Running Sum
• Running sum counts values in a loop to give a total
Initialise the sum variable before the loop
– Increment the sum variable with a variable inside the loop
(this value may be different at every loop iteration)
– Print the final sum after the loop
e.g. $sum = 0; // initialise as 0
for ($i = 1; $i<=10; $i=$i+1){
$sum= $sum + $i; // increment by value - $i
}
print $sum; // prints final count value – 55
// this sums 1+2+3+4+5+6+7+8+9+10
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Exercise 5 – to try
A. Use a for loop to print the odd numbers from 1
to 21 (rember Exercise 3A) and add these
numbers together to give a total (running sum)
B. Use a while loop to print numbers 1,2,3 etc
adding the numbers together (running sum)
while the total is less than 50 (while condition)
and also count how many times the loop goes
round (using loop count) printing sum & loop
count
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Some Basic Maths Functions
•
•
•
•
•
Absolute value
Square root,
Round,
Integer checker and
Random number generation
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abs() Function
• The absolute value function takes a single
numerical argument and returns its
absolute value (disregards negative sign).
• For example, the following
$x=abs(-5);
$y=abs(42);
print "x=$x y=$y";
• Will output
– x=5 y=42
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sqrt() Function
• The square root function takes a single
numerical argument and returns its square
root.
• For example, the following
– $x=sqrt(25);
– $y=sqrt(24);
– print "x=$x y=$y";
• Will output
– x=5 y=4.898979485566
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round() Function
• The round function takes a single numerical
argument and returns the number rounded
up or down to the nearest integer.
• For example, the following
– $x=round(-5.456);
– $y=round(3.7342);
– print "x=$x y=$y";
• Will output x=-5 y=4
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round() Function
• You can include 2nd argument to define
the number of digits after the decimal
point to round to.
• For example,
• $x=round(-5.456,2);
• $y=round(3.7342,3);
• print "x=$x y=$y";
• would output
– x=-5.46 y=3.734
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is_numeric() Function
• is_numeric() is useful for determining whether a
variable is a valid number or a numeric string.
– It returns true or false.
• Consider the following example...
if (is_numeric($input)) {
print "Got Valid Number=$input";
} else {
print "Not Valid Number=$input";
}
• If $input was "6" then would output:
Got Valid Number=6
• If $input was "Happy" then would output:
Not Valid Number=Happy
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rand() Function
• Use rand( ) to generate a random number.
– You can use random numbers to simulate a dice roll or a coin
toss or to randomly select an advertisement banner to display.
• rand( ) typically uses 2 arguments to define the
range of numbers it should return (min and max
limits),
– For example the following returns a number 1 - 15
• $num = rand(1, 15);
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Coin flip using rand( )
• Rand( ) can be used to generate a random coin flip
$flip = rand(0,1);
if ($flip == 0){
print "Your random coin flip is heads";
}
elseif ($flip == 1){
print "Your random coin flip is tails";
}
• The random number generated is 0 or 1 – these can be
assigned as heads or tails
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Exercise 6 – flip a coin
Headsortails.html
Given the web page shown on pages 35& 36
Create a php script gotflip.php
Gotflip.php
- Gets the user choice from radio button named "pick"
with heads having value = 0 & tails having value =1
- use rand( ) to generate a random flip
- check whether the user pick is correct or not
- print the result
- now change the program to display the user choice as heads
or tails compared with the random flip result of heads or tails
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Headsortails.html
<html><head><title> Coin Flip!</title></head><body>
<font color="BLUE" size="4"> Please Pick Heads or Tails! </font>
<form action="gotflip.php" method="post"><br>
<input name="pick" value="0" type="radio">Heads<br>
<input name="pick" value="1" type="radio">Tails<br><br>
<input type="submit" value="Click To Submit" ><br><br>
<input value="Erase and Restart" type="reset">
</form></body></html>
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Headortails Web Page
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Advanced Coin Flip – Exercise7A
A. Create a PHP script to flip a coin 20 times and count
how many flips are heads and how many are tails
– Use a for loop (inside which the coin is flipped and count
made)
– Use the rand function to generate a coin flip
– Use an if statement to check if the flip is heads or tails
– Use a count (e.g. $numheads = $numheads +1;) to count
the number of heads & tails as each loop goes round (must
initialise this variable to 0 before the for loop)
– Finally print out the total number of heads & the total
number of tails
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Advanced Coin Flip - Exercise 7B
• B. Now create a PHP script to flip a coin until either
20 heads or 20 tails have been flipped
–
–
–
–
Use a while loop (what is the condition?)
Count the number of heads and tails as before
Count the total number of flips (different count variable)
Finally print out the number of heads and tails and total
number of flips
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Dice Roll using rand( )
• Rand( ) can be used to generate a random dice
throw
$roll = rand(1,6);
print "Your random dice roll is $roll";
• The random number generated in this case can be
a 1, 2, 3, 4, 5, or 6.
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Exercise 8A – dice roll
• Change the coin toss program to a dice roll
i.e. guessnumber.html & checkguess.php
guessnumber.html
- Displays a form with radio buttons to choose 1 – 6
checkguess.php
- receives the user choice
- generates a random dice roll
- compares the choice with the random role
- prints the result along with the choice and the random roll
values
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Exercise 8B - Diceroll_twenty
Write a php script to:
- Assign a value to a guess
- Roll one dice 20 times
- Each time compare the guess with the random roll
- Keep a count of how many times the guess is right
- Print out the guess value along with the number of correct
guesses
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Exercise 8C - RollsUntilWin
Write a php script to:
- Assign a value to a guess
- Roll one dice until the correct answer is guessed
- Print out
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Functions
• As well as built-in predefined functions you can
specify your own functions
• This allows efficient code reuse if you need to use
the functionality several times (reusability)
• In larger programs functions are used to separate
different areas of functionality and provide a good
structure to the code
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Writing Your Own Functions
• Use the following general format
function function_name( ) {
set of statements
}
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Returning Values
• Your functions can return data to the calling
script.
– For example, your functions can return the
results of a computation.
– You can use the PHP return statement to return a
value to the calling script statement:
return $result;
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Example function – get the larger
of two numbers
<?php
function get_larger( $num1, $num2 ) {
if ($num1 > $num2) {
return($num1);
} else {
return($num2);
}
}
$larger= get_larger(10, 20);
print “larger number is $larger”;
?>
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Exercise 9
• Create a function to:
– Input 3 numbers
– Calculate the average of the numbers
– Return the average
• Use the function in a PHP script to
– Use the function to average 4, 10 & 17
– Print the average value
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Using External Script Files
• Sometime you will want to use scripts from external files.
• PHP supports 2 related functions:
– <?php
require ("header.php");
include ("footer.php");
….
?>
The require() function
produces a fatal
error if it can’t
insert the specified file.
The include() function
produces a warning
if it can’t
insert the specified file.
• Both search for the file named within the double quotation
marks and insert its PHP, HTML, or JavaScript code into the
current file.
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Use of include( ) & require( )
• Include( ) & require( ) used to
–
–
–
–
Create functions
Headers
Footers
Elements to be used on multiple pages
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Simple include( ) example
header.php
<?php
$colour = "green";
$items= "bottles";
?>
test.php
<?php
print "10 $colour $items";
// prints 10
include ("header.php");
print
?>
"10 $colour $items";
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// prints 10 green bottles
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