Table of Contents
PHP is one of the programming languages that are very easy to learn. You can learn the basic in just a few days. This mini series will show you how. In this part, you will learn all you need about conditional statements, loops and break, continue, include and require statements. Make another step towards reaching PHP mastery!
Getting Started with PHP the Easy Way Part 1 (Variables & Data types).
Getting Started with PHP the Easy Way Part 3 (OOP Pt1).
Getting Started with PHP the Easy Way Part 4 (OOP Pt2 and Beyond).
PHP and control structures
Let’s start with set of PHP goodies called control structures. These goodies allows you to write code that will react differently depending on current situation. This can be anything. For example, it can be a change that occurred somewhere in the code or that was caused by user input. The primary types of control structures are conditional statements and loops. Let’s take a look at them.
Conditional statements
Imagine that you want to execute two different actions. What action should be executed depends on some condition. This is where you can use something called conditional statement, also called if else statement. In order to use this, you need two things. First, you need to specify the condition. Second, you need to specify the first action to be executed, if the condition is true.
When you are done with that, you can also specify the second action to be executed, if the condition is false. However, this is not necessary. In other words, you can emit the else part.
// Default if statement (with else part)
<?php
if (condition) {
// Code to be executed;
}
?>
// Default if else statement
<?php
if (condition) {
// Code to be executed;
} else {
// Code to be executed;
}
?>
// Simple example of if else statement
<?php
$x = 3;
$y = 21;
if ($x <= $y) {
echo "Variable 'x' is smaller or equal than variable 'y'";
} else {
echo "Variable 'x' is bigger than variable 'y'";
}
// Outputs "Variable 'x' is smaller or equal than variable 'y'"
?>
Okay, but what if you want something more complex? For example, what if you want to specify another condition if the first one is false? In that case, you can do two things. First, you use another if else statement, nested inside the else. Second, you can use elseif statement. This statement allows you to use more than one condition without the nesting one statement inside another.
// Example with nested statement
<?php
$x = 34;
$y = 21;
$z = 51;
if ($x <= $y) {
echo "Variable 'x' is smaller or equal than variable 'y'";
} else {
if ($x <= $z) {
echo "Variable 'x' is bigger than variable 'y' and smaller or equal than variable 'z'";
} else {
echo "Variable 'x' is bigger than variable 'y' and 'z'";
}
echo "Variable 'x' is bigger than variable 'y'";
}
// Outputs "Variable 'x' is bigger than variable 'y' and smaller or equal than variable 'z'"
?>
// Example with elseif statement
<?php
$x = 34;
$y = 21;
$z = 51;
if ($x <= $y) {
echo "Variable 'x' is smaller or equal than variable 'y'";
} elseif ($x <= $z) {
echo "Variable 'x' is bigger than variable 'y' and smaller or equal than variable 'z'";
} else {
echo "Variable 'x' is bigger than variable 'y' and 'z'";
}
// Outputs "Variable 'x' is bigger than variable 'y' and smaller or equal than variable 'z'"
?>
One benefit of using the elseif statement is that it is cleaner than the one with nested if else statement. This may not be as obvious one the example above. However, imagine that you have three, four or even more conditions. Then, your code could quickly become barely readable.
// Example with nested statement
<?php
if (condition) {
... some action ...
} else {
if (condition) {
... some action ...
} else {
if (condition) {
... some action ...
} else {
if (condition) {
... some action ...
} else {
... some action ...
}
}
}
... some action ...
}
?>
// Example with elseif statement
<?php
if (condition) {
... some action ...
} elseif (condition) {
... some action ...
} elseif (condition) {
... some action ...
} elseif (condition) {
... some action ...
} else {
... some action ...
}
?>
Switch
Conditional statements, or the if else and elseif, are quite useful and powerful. However, there will be situations when you will need something better. Imagine you want to test for a specific case to execute specific code. The problem is that this case has many variants. For example, imagine a calendar app where the case you want to test for is the day of the week.
Sure. You can still use elseif. However, it is not the most elegant solution. A better option, offered by PHP, is to use switch statement. switch allows to test for a specific expression, usually some variable. Next, it compares the value of the expression with the value of each case defined inside it. If it finds a match, the block of code inside that case is executed.
What if none of the case fits the expression? Then, there are two options. First, switch will go test all cases, finds no match, and nothing happens. Or, you can add additional case called default. Then, if switch doesn’t find any match, it will execute the code inside this default case. One last thing. Every case should be ended with break keyword.
You can think about this as a brake. It will prevent switch from automatically running into the next case. If you forget the break, PHP will automatically continue through the next case, even when the case doesn’t match. If you don’t have any break inside your switch, PHP will run through all cases and execute code in all of them.
Let’s use the example of calendar app again. In this example, the expression, or the variable, switch will test will be the day of the week. Next, there will be case for each day, with additional default case if the day doesn’t exist. So, eight cases in total. Remember to include the break statement at the end of every case.
// Default switch statement
<?php
switch (expression) {
case value1:
//code to be executed if expression = value1
break;
case value2:
//code to be executed if expression = value2
break;
...
default:
// code to be executed if 'expression' doesn't fit any case
}
?>
// Simple example of calendar app with switch statement
<?php
$day = "fri";
switch ($day) {
case "mon":
echo "Today is Monday.";
break;
case "tue":
echo "Today is Tuesday.";
break;
case "wed":
echo "Today is Wednesday.";
break;
case "thu":
echo "Today is Thursday.";
break;
case "fri":
echo "Today is Friday.";
break;
case "sat":
echo "Today is Saturday.";
break;
case "sun":
echo "Today is Sunday.";
break;
default:
echo "This day doesn't seem to exist.";
}
// Outputs "Today is Friday."
?>
One last thing. Let’s take a look at what would happen if you forgot to add the break statement in each case. As you will see, switch will cycle through every case, and check if the expression fits the variable, the day. If not, it will skip the case as. So for good. What happens next? The switch will not be terminated when it finds a match.
Instead, it will go to the next case, after the match, and execute the code inside this case. And, the same will happen with every case that follows the match. switch will execute code inside all these cases. In the case of the calendar app, it will print message for every day starting with the day that matches the day specified in $day variable.
// Example of switch statement without break statement
<?php
$day = "fri";
switch ($day) {
case "mon":
echo "Today is Monday.";
case "tue":
echo "Today is Tuesday.";
case "wed":
echo "Today is Wednesday.";
case "thu":
echo "Today is Thursday.";
case "fri":
echo "Today is Friday.";
case "sat":
echo "Today is Saturday.";
case "sun":
echo "Today is Sunday.";
default:
echo "This day doesn't seem to exist.";
}
// Outputs "Today is Friday.Today is Saturday.Today is Sunday.This day doesn't seem to exist."
?>
The while loop
Aside to conditional statements, you can also use loops. These loops can be quite useful when you want the same block of code to run over and over again. You don’t have to copy the same code over and over again. Instead, you can use loops to do the work for you. You will probably agree that this will result in much cleaner and more elegant code.
The first loop PHP offers is while loop. The way while works is very simple. It executes a block of code as long as the condition you specified is true. When the condition evaluates to false, the while loop is terminated. This also makes while loop potentially dangerous. Imagine you forget to add code that will change the condition at some point. What will happen?
The while loop will never stop. It will continue executing the code over and over again. In other words, you will create something called infinite loop. In the example below, you will create $num variable and set its value to “1”. Then, you will use while loop to output the value of this variable, and increase its value, as long as the value is smaller than 7.
Increasing the value of $num variable will ensure that the condition used for while will evaluate to false at some point. Without this, you would create the infinite loop you read about above. How? If you don’t increase the value $num variable, it will be always smaller than 7 and the condition for while loop will always evaluate to true.
// Default while loop
<?php
while (condition) {
// your code to be executed;
}
?>
// A simple example of while loop
<?php
$num = 1;
while ($num < 7) {
echo "The number is $num <br />"; // Output current value of $num variable
$num++; // Increase the value of $num variable
}
?>
The do-while loop
PHP offers a more advanced version of while loop. This one is called do-while loop. What is the difference between the while and do-while loop? The do-while loop will always execute the block of code at least once. It doesn’t matter if the condition you specified is true or false. The do-while loop executes the code before it checks the condition.
If the condition is evaluates to false, it will not run again. Otherwise, it will repeat the loop as long as the condition evaluates to true. Just like a regular while loop.
// Default do-while loop
<?php
do {
// Code here will be executed at least once;
} while (condition);
?>
// A simple example of do-while loop
<?php
$num = 3;
do {
echo "The number is " . $num . "<br/>";
$num++;
} while($num <= 5);
//Output
// The number is 3
// The number is 4
// The number is 5
?>
The for loop
Next loop you can use in PHP is for loop. This loop is a good choice when you know how many times the code inside the loop should be executed. The for loop requires three parameters. These parameters are init (starting loop counter value), test (test evaluated each time the loop is iterated, continuing if true and ending if false) and increment (increases the loop counter value).
When you use a for loop, there are few things to remember. First, each of the parameters can be empty. Second, each of the parameters can also contain multiple expressions. These expressions must be separated with commas. Third,
all parameters of the for loop must be separated with semicolons. Let’s take a look at a simple example of for loop.
The loop in the example below first creates new variable $i and sets its value to 0. Then, it checks for the condition, in this case if $i < 6. If the condition is true, loop runs the code. After that, the loop automatically increments the $i variable ($i++) and next iteration follows.
// Default for loop
<?php
for (init; test; increment) {
// Code to be executed;
};
?>
// Simple example of for loop
<?php
for ($i = 0; $i < 6; $i++) {
echo "Value of i: ". $i . "<br />";
}
// Outputs "Value of i: 0."
// Outputs "Value of i: 1."
// Outputs "Value of i: 2."
// Outputs "Value of i: 3."
// Outputs "Value of i: 4."
// Outputs "Value of i: 5."
?>
The foreach loop
The foreach is the last loop you can use in PHP. Three thing you must know about this loop. First, this loop works only on arrays. Second, you can use it only to loop through key/value pair inside the array. Third, you can write foreach loop using two different forms of syntax. As you will see, the difference between those two forms is very small, but the result can be significant.
The first “form” of a syntax loops over the array. On each iteration, the value of the current element is assigned to $value. Then, the array pointer is moved by one. This repeats until the loop reaches the last array element. The second “form” will do the same as first, but it will also assign the current element’s key to the $key variable, on each iteration.
// Default foreach loop
<?php
foreach (array as $value) {
// code to be executed;
}
// or
foreach (array as $key => $value) {
// code to be executed;
}
?>
// Simple example of foreach loop (the first form)
<?php
$names = array("Adam", "Cindy", "Eric", "Geraldo", "Massimo");
foreach ($names as $name) {
echo $name.'<br />';
}
// Outputs:
// Adam
// Cindy
// Eric
// Geraldo
// Massimo
?>
// Simple example of foreach loop (the second form)
<?php
$names = array("Adam", "Cindy", "Eric", "Geraldo", "Massimo");
foreach ($names as $name => $value) {
echo "Value of \$name is:" . $name . " and value of \$value is:" . $value . ".<br />";
}
// Outputs:
// Value of $name is:0 and value of $value is:Adam.
// Value of $name is:1 and value of $value is:Cindy.
// Value of $name is:2 and value of $value is:Eric.
// Value of $name is:3 and value of $value is:Geraldo.
// Value of $name is:4 and value of $value is:Massimo.
?>
The continue statement
One last thing related to control structures. There might be a situation when you will want to use a loop, but you will also want to skip some code execution in some cases. This is exactly when continue statement will be useful. Put simply, when you use continue statement inside a loop structure, you can skip code execution in current loop iteration.
So far, it looks like what break statement does. However, continue will not stop or terminate the loop. The loop will continue with the next iteration. Well, if there is one. Let’s take a look at a simple example. The for loop below will iterate through numbers in range from 0 to 9. Next, there is an if statement that will check if the number in current iteration is even or odd.
When the number is even, the condition in if statement is true, continue statement will be executed. This will cause the for loop to skip the code that follows the if statement. In other words, the for loop will not output the number if the number is even. Instead, it will continue with next iteration.
// Example of continue statement
<?php
for ($num = 0; $num < 10; $num++) {
if ($num % 2 == 0) {
continue;
}
echo $num . ', ';
}
// Output: 1, 3, 5, 7, 9,
?>
Include & require statements
When you work on a big project, the codebase can quickly become quite large. This will make the code harder to work with, organize and maintain. Fortunately, PHP can help you here. What you can do is to use include and require statements. These statements allow you to insert content inside one PHP file into another, before the server executes the code.
This is a common practice in WordPress development. Developers create small PHP components for headers, footers, sidebars and other parts of the website. Then, they include or require the component when they need it. This makes their work quite easy and fast. When the developer needs to change some PHP component, he has to update only the file with that component file. The change will propagate everywhere.
What is the difference between include and require? They are almost identical. The difference is that when you use require to include some file, the script will produce an error when the file is not found. On the other hand, if you use include, it will skip the file and code will continue to execute. So, if some file is necessary, use require. Otherwise, use include.
// File "header.php"
<?php
echo '<h1>Welcome</h1>';
?>
// File index.html
<html>
<head></head>
<body>
<!-- Include the content of "header.php" -->
<?php include "header.php"; ?>
<!-- Or, require it -->
<?php require "header.php"; ?>
</body>
</html>
Epilogue: Getting Started with PHP the Easy Way Pt2
Congratulations! You’ve just finished the second part of this mini series about PHP. Today, you’ve learned about conditional statements, or the if else, elseif and switch. Then, you’ve learned about while, do-while, for and foreach loops. At the end, you’ve also learned about break, continue, include and require statements. What’s next?
In the third and final part, you will learn about PHP functions, OOP and classes and how to work with files. This will provide you with a solid foundation to start using PHP in your projects. It will also make it easier for you to complete your PHP learning path and reach PHP mastery. Now, practice what you’ve learn today as well as in the first part. Thank you for your time.
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