Very often when you write code, you want to perform different actions for different conditions. You can use conditional statements in your code to do this.
In PHP we have the following conditional statements:
ifstatement - executes some code if one condition is trueif...elsestatement - executes some code if a condition is true and another code if that condition is falseif...elseif...elsestatement - executes different codes for more than two conditionsswitchstatement - selects one of many blocks of code to be executed
PHP - The if Statement
The if statement executes some code if one condition is true.
Syntax
if (condition) {
code to be executed if condition is true;
}Example
Output "Have a good day!" if the current time (HOUR) is less than 20:
<?php
$t = date("H");
if ($t < "20") {
echo "Have a good day!";
}
?>PHP - The if...else Statement
The if...else statement executes some code if a condition is true and another code if that condition is false.
Syntax
if (condition) {
code to be executed if condition is true;
} else {
code to be executed if condition is false;
}Example
Output "Have a good day!" if the current time is less than 20, and "Have a good night!" otherwise:
<?php
$t = date("H");
if ($t < "20") {
echo "Have a good day!";
} else {
echo "Have a good night!";
}
?>PHP - The if...elseif...else Statement
The if...elseif...else statement executes different codes for more than two conditions.
Syntax
if (condition) {
code to be executed if this condition is true;
} elseif (condition) {
code to be executed if first condition is false and this condition is true;
} else {
code to be executed if all conditions are false;
}Example
Output "Have a good morning!" if the current time is less than 10, and "Have a good day!" if the current time is less than 20. Otherwise it will output "Have a good night!":
<?php
$t = date("H");
if ($t < "10") {
echo "Have a good morning!";
} elseif ($t < "20") {
echo "Have a good day!";
} else {
echo "Have a good night!";
}
?>PHP - The switch Statement
The switch statement will be explained in the next chapter.
The switch statement is used to perform different actions based on different conditions.
The PHP switch Statement
Use the switch statement to select one of many blocks of code to be executed.
Syntax
switch (n) {
case label1:
code to be executed if n=label1;
break;
case label2:
code to be executed if n=label2;
break;
case label3:
code to be executed if n=label3;
break;
...
default:
code to be executed if n is different from all labels;
}This is how it works: First we have a single expression n (most often a variable), that is evaluated once. The value of the expression is then compared with the values for each case in the structure. If there is a match, the block of code associated with that case is executed. Use break to prevent the code from running into the next case automatically. The default statement is used if no match is found.
Example
<?php
$favcolor = "red";
switch ($favcolor) {
case "red":
echo "Your favorite color is red!";
break;
case "blue":
echo "Your favorite color is blue!";
break;
case "green":
echo "Your favorite color is green!";
break;
default:
echo "Your favorite color is neither red, blue, nor green!";
}
?>PHP Loops
Often when you write code, you want the same block of code to run over and over again a certain number of times. So, instead of adding several almost equal code-lines in a script, we can use loops.
Loops are used to execute the same block of code again and again, as long as a certain condition is true.
In PHP, we have the following loop types:
while- loops through a block of code as long as the specified condition is truedo...while- loops through a block of code once, and then repeats the loop as long as the specified condition is truefor- loops through a block of code a specified number of timesforeach- loops through a block of code for each element in an array
The while loop - Loops through a block of code as long as the specified condition is true.
The PHP while Loop
The while loop executes a block of code as long as the specified condition is true.
Syntax
while (condition is true) {
code to be executed;
}Examples
The example below displays the numbers from 1 to 5:
Example
<?php
$x = 1;
while($x <= 5) {
echo "The number is: $x <br>";
$x++;
}
?>Example Explained
- $x = 1; - Initialize the loop counter ($x), and set the start value to 1
- $x <= 5 - Continue the loop as long as $x is less than or equal to 5
- $x++; - Increase the loop counter value by 1 for each iteration
This example counts to 100 by tens:
Example
<?php
$x = 0;
while($x <= 100) {
echo "The number is: $x <br>";
$x+=10;
}
?>Example Explained
- $x = 0; - Initialize the loop counter ($x), and set the start value to 0
- $x <= 100 - Continue the loop as long as $x is less than or equal to 100
- $x+=10; - Increase the loop counter value by 10 for each iteration
The do...while loop - Loops through a block of code once, and then repeats the loop as long as the specified condition is true.
The PHP do...while Loop
The do...while loop will always execute the block of code once, it will then check the condition, and repeat the loop while the specified condition is true.
Syntax
do {
code to be executed;
} while (condition is true);
code to be executed;
} while (condition is true);
Examples
The example below first sets a variable $x to 1 ($x = 1). Then, the do while loop will write some output, and then increment the variable $x with 1. Then the condition is checked (is $x less than, or equal to 5?), and the loop will continue to run as long as $x is less than, or equal to 5:
Example
<?php
$x = 1;
do {
echo "The number is: $x <br>";
$x++;
} while ($x <= 5);
?>Note: In a do...while loop the condition is tested AFTER executing the statements within the loop. This means that the do...while loop will execute its statements at least once, even if the condition is false. See example below.
<?php
$x = 1;
do {
echo "The number is: $x <br>";
$x++;
} while ($x <= 5);
?>Note: In a do...while loop the condition is tested AFTER executing the statements within the loop. This means that the do...while loop will execute its statements at least once, even if the condition is false. See example below.
This example sets the $x variable to 6, then it runs the loop, and then the condition is checked:
Example
<?php
$x = 6;
do {
echo "The number is: $x <br>";
$x++;
} while ($x <= 5);
?>
<?php
$x = 6;
do {
echo "The number is: $x <br>";
$x++;
} while ($x <= 5);
?>The PHP for Loop
The for loop is used when you know in advance how many times the script should run.
Syntax
for (init counter; test counter; increment counter) {
code to be executed for each iteration;
}
code to be executed for each iteration;
}
Parameters:
- init counter: Initialize the loop counter value
- test counter: Evaluated for each loop iteration. If it evaluates to TRUE, the loop continues. If it evaluates to FALSE, the loop ends.
- increment counter: Increases the loop counter value
Examples
The example below displays the numbers from 0 to 10:
Example
<?php
for ($x = 0; $x <= 10; $x++) {
echo "The number is: $x <br>";
}
?>
<?php
for ($x = 0; $x <= 10; $x++) {
echo "The number is: $x <br>";
}
?>Example Explained
- $x = 0; - Initialize the loop counter ($x), and set the start value to 0
- $x <= 10; - Continue the loop as long as $x is less than or equal to 10
- $x++ - Increase the loop counter value by 1 for each iteration
This example counts to 100 by tens:
Example
<?php
for ($x = 0; $x <= 100; $x+=10) {
echo "The number is: $x <br>";
}
?>
<?php
for ($x = 0; $x <= 100; $x+=10) {
echo "The number is: $x <br>";
}
?>
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