loop in loop php
Loops in PHP are used to execute the same block of code a specified number of times. PHP supports following four loop types.
for − loops through a block of code a specified number of times.
while − loops through a block of code if and as long as a specified condition is true.
do. while − loops through a block of code once, and then repeats the loop as long as a special condition is true.
foreach − loops through a block of code for each element in an array.
We will discuss about continue and break keywords used to control the loops execution.
The for loop statement
The for statement is used when you know how many times you want to execute a statement or a block of statements.
Syntax
Example
The following example makes five iterations and changes the assigned value of two variables on each pass of the loop −
This will produce the following result −
The while loop statement
The while statement will execute a block of code if and as long as a test expression is true.
If the test expression is true then the code block will be executed. After the code has executed the test expression will again be evaluated and the loop will continue until the test expression is found to be false.
Syntax
Example
This example decrements a variable value on each iteration of the loop and the counter increments until it reaches 10 when the evaluation is false and the loop ends.
This will produce the following result −
The do. while loop statement
Syntax
Example
The following example will increment the value of i at least once, and it will continue incrementing the variable i as long as it has a value of less than 10 −
This will produce the following result −
The foreach loop statement
Syntax
Example
Try out following example to list out the values of an array.
This will produce the following result −
The break statement
The PHP break keyword is used to terminate the execution of a loop prematurely.
The break statement is situated inside the statement block. It gives you full control and whenever you want to exit from the loop you can come out. After coming out of a loop immediate statement to the loop will be executed.
Example
In the following example condition test becomes true when the counter value reaches 3 and loop terminates.
This will produce the following result −
The continue statement
The PHP continue keyword is used to halt the current iteration of a loop but it does not terminate the loop.
Just like the break statement the continue statement is situated inside the statement block containing the code that the loop executes, preceded by a conditional test. For the pass encountering continue statement, rest of the loop code is skipped and next pass starts.
Example
In the following example loop prints the value of array but for which condition becomes true it just skip the code and next value is printed.
Loop in loop php
(PHP 4, PHP 5, PHP 7, PHP 8)
for loops are the most complex loops in PHP. They behave like their C counterparts. The syntax of a for loop is:
The first expression ( expr1 ) is evaluated (executed) once unconditionally at the beginning of the loop.
At the end of each iteration, expr3 is evaluated (executed).
Consider the following examples. All of them display the numbers 1 through 10:
Of course, the first example appears to be the nicest one (or perhaps the fourth), but you may find that being able to use empty expressions in for loops comes in handy in many occasions.
PHP also supports the alternate «colon syntax» for for loops.
It’s a common thing to many users to iterate through arrays like in the example below.
The above code can be slow, because the array size is fetched on every iteration. Since the size never changes, the loop be easily optimized by using an intermediate variable to store the size instead of repeatedly calling count() :
User Contributed Notes 22 notes
Looping through letters is possible. I’m amazed at how few people know that.
returns: R S T U V W X Y Z AA AB AC
The point about the speed in loops is, that the middle and the last expression are executed EVERY time it loops.
So you should try to take everything that doesn’t change out of the loop.
Often you use a function to check the maximum of times it should loop. Like here:
You can use strtotime with for loops to loop through dates
Remember that for-loops don’t always need to go ‘forwards’. For example, let’s say I have the following code:
PHP Loops
In this tutorial you will learn how to repeat a series of actions using loops in PHP.
Different Types of Loops in PHP
Loops are used to execute the same block of code again and again, as long as a certain condition is met. The basic idea behind a loop is to automate the repetitive tasks within a program to save the time and effort. PHP supports four different types of loops.
You will also learn how to loop through the values of array using foreach() loop at the end of this chapter. The foreach() loop work specifically with arrays.
PHP while Loop
The while statement will loops through a block of code as long as the condition specified in the while statement evaluate to true.
Example
PHP do…while Loop
The do-while loop is a variant of while loop, which evaluates the condition at the end of each loop iteration. With a do-while loop the block of code executed once, and then the condition is evaluated, if the condition is true, the statement is repeated as long as the specified condition evaluated to is true.
Example
Difference Between while and do…while Loop
The while loop differs from the do-while loop in one important way — with a while loop, the condition to be evaluated is tested at the beginning of each loop iteration, so if the conditional expression evaluates to false, the loop will never be executed.
With a do-while loop, on the other hand, the loop will always be executed once, even if the conditional expression is false, because the condition is evaluated at the end of the loop iteration rather than the beginning.
PHP for Loop
The for loop repeats a block of code as long as a certain condition is met. It is typically used to execute a block of code for certain number of times.
The parameters of for loop have following meanings:
Example
PHP foreach Loop
The foreach loop is used to iterate over arrays.
The following example demonstrates a loop that will print the values of the given array:
Example
There is one more syntax of foreach loop, which is extension of the first.
Differences between a while loop and a for loop in PHP?
I’m reading an ebook on PHP right now, and the author noted that the difference between a while loop and a for loop is that the for loop will count how many times it runs.
But wouldn’t this be the same as
Or is there some other differences that he didn’t point out? (Aside from using while loop for when you’re unsure of how long the condition will remain true, such as selecting rows from a database)
I mean, if that’s the only difference, can’t I just not use the for loop and use the while loop instead?
6 Answers 6
«For» expresses your intentions more clearly
Functionally, your two examples are the same. But they express different intentions.
You can use one when you mean the other, but it’s harder to read the code.
Some other reasons why for is preferable here
Don’t forget foreach
Faster to type, easier to read.
Can you? Yes, certainly. But whether or not you should is an entirely different question.
The for loop is more readable in this scenario, and is definitely the convention you’ll find used within virtually every language that has looping directives. If you use the while loop, people are going to wonder why you didn’t use a for loop.
Functionally, a for loop is equivalent to a while loop; that is, each can be rewritten as the other with no change to the outcome or side effects. However, each has different connotations. A while loop runs while a condition holds; the condition is static, though circumstances change. A for loop runs over a sequence. The difference is important to programmers but not programs, just as choice of variables names are important to programmers even though they can be changed to produce functionally equivalent code. One loop construct will make more sense than the other, depending on the situation.
is basically the same as a while-loop structured like this:
While you could technically use one or the other, there are situations where while works better than for and vice-versa.
The Main Difference Between for() and While() is that we have to define the limit or count but in while() loop we don’t define limit or count it works until reached the last item
FOR LOOP Initialization may be either in loop statement or outside the loop. It is normally used when the number of iterations is known. Condition is a relational expression. It is used when initialization and increment is simple. for ( init ; condition ; iteration )
WHILE LOOP Initialization is always outside the loop. It is normally used when the number of iterations is unknown. Condition may be expression or non-zero value. It is used for complex initialization. while ( condition )
PHP Control Structures and Loops: if, else, for, foreach, while, and More
Today, we’re going to discuss control structures and loops in PHP. I’ll show you how to use all the main control structures that are supported in PHP, like if, else, for, foreach, while, and more.
What Is a Control Structure?
In simple terms, a control structure allows you to control the flow of code execution in your application. Generally, a program is executed sequentially, line by line, and a control structure allows you to alter that flow, usually depending on certain conditions.
Control structures are core features of the PHP language that allow your script to respond differently to different inputs or situations. This could allow your script to give different responses based on user input, file contents, or some other data.
The following flowchart explains how a control structure works in PHP.
As you can see in the above diagram, first a condition is checked. If the condition is true, the conditional code will be executed. The important thing to note here is that code execution continues normally after conditional code execution.
Let’s consider the following example.
In the above example, the program checks whether or not the user is logged in. Based on the user’s login status, they will be redirected to either the Login page or the My Account page. In this case, a control structure ends code execution by redirecting users to a different page. This is a crucial ability of the PHP language.
PHP supports a number of different control structures:
Let’s take a look at a few of these control structures with examples.
Learning PHP Control Structures
In the previous section, we learned the basics of control structures in PHP and their usefulness in application development. In this section, we’ll go through a couple of important control structures that you’ll end up using frequently in your day-to-day application development.
PHP If Statement
The if construct allows you to execute a piece of code if the expression provided along with it evaluates to true.
Let’s have a look at the following example to understand how it actually works.
The above example should output the Your age is greater than 30! message since the expression evaluates to true. In fact, if you want to execute only a single statement, the above example can be rewritten without brackets, as shown in the following snippet.
On the other hand, if you have more than one statement to execute, you must use brackets, as shown in the following snippet.
PHP Else Statement
In the previous section, we discussed the if construct, which allows you to execute a piece of code if the expression evaluates to true. On the other hand, if the expression evaluates to false, it won’t do anything. More often than not, you also want to execute a different code snippet if the expression evaluates to false. That’s where the else statement comes into the picture.
You always use the else statement in conjunction with an if statement. Basically, you can define it as shown in the following pseudo-code.
Let’s revise the previous example to understand how it works.
So when you have two choices, and one of them must be executed, you can use the if-else construct.
PHP Else If Statement
We can consider the elseif statement as an extension to the if-else construct. If you’ve got more than two choices to choose from, you can use the elseif statement.
Let’s study the basic structure of the elseif statement, as shown in the following pseudo-code.
Again, let’s try to understand it using a real-world example.
As you can see in the above example, we have multiple conditions, so we’ve used a series of elseif statements. In the event that all if conditions evaluate to false, it executes the code provided in the last else statement.
PHP Switch Statement
The switch statement is somewhat similar to the elseif statement which we’ve just discussed in the previous section. The only difference is the expression which is being checked.
In the case of the elseif statement, you have a set of different conditions, and an appropriate action will be executed based on a condition. On the other hand, if you want to compare a variable with different values, you can use the switch statement.
As usual, an example is the best way to understand the switch statement.
Finally, if you want to execute a piece of code if the variable’s value doesn’t match any case, you can define it under the default block. Of course, it’s not mandatory—it’s just a way to provide a default case.
So that’s the story of conditional control structures. We’ll discuss loops in PHP in the next section.
Loops in PHP
Loops in PHP are useful when you want to execute a piece of code repeatedly until a condition evaluates to false. So code is executed repeatedly as long as a condition evaluates to true, and as soon as the condition evaluates to false, the script continues executing the code after the loop.
The following flowchart explains how loops work in PHP.
As you can see in the above screenshot, a loop contains a condition. If the condition evaluates to true, the conditional code is executed. After execution of the conditional code, control goes back to the loop condition, and the flow continues until the condition evaluates to false.
In this section, we’ll go through the different types of loops supported in PHP.
While Loop in PHP
The while loop is used when you want to execute a piece of code repeatedly until the while condition evaluates to false.
You can define it as shown in the following pseudo-code.
Let’s have a look at a real-world example to understand how the while loop works in PHP.
If you’re familiar with the Fibonacci series, you might recognize what the above program does—it outputs the Fibonacci series for the first ten numbers. The while loop is generally used when you don’t know the number of iterations that are going to take place in a loop.
Do-While Loop in PHP
The do-while loop is very similar to the while loop, with the only difference being that the while condition is checked at the end of the first iteration. Thus, we can guarantee that the loop code is executed at least once, irrespective of the result of the while expression.
Let’s have a look at the syntax of the do-while loop.
Let’s go through a real-world to understand possible cases where you can use the do-while loop.
In the above example, we’re trying to read a file line by line. Firstly, we’ve opened a file for reading. In our case, we’re not sure if the file contains any content at all. Thus, we need to execute the fgets function at least once to check if a file contains any content. So we can use the do-while loop here. do-while evaluates the condition after the first iteration of the loop.
For Loop in PHP
Generally, the for loop is used to execute a piece of code a specific number of times. In other words, if you already know the number of times you want to execute a block of code, it’s the for loop which is the best choice.
Let’s have a look at the syntax of the for loop.
The expr1 expression is used to initialize variables, and it’s always executed. The expr2 expression is also executed at the beginning of a loop, and if it evaluates to true, the loop code is executed. After execution of the loop code, the expr3 is executed. Generally, the expr3 is used to alter the value of a variable which is used in the expr2 expression.
Let’s go through the following example to see how it works.
For Each in PHP
The foreach loop is used to iterate over array variables. If you have an array variable, and you want to go through each element of that array, the foreach loop is the best choice.
Let’s have a look at a couple of examples.
Breaking Out of the Loop
You can also use break to get out of multiple nested loops by supplying a numeric argument. For example, using break 3 will break you out of 3 nested loops. However, you cannot pass a variable as the numeric argument if you are using a PHP version greater than or equal to 5.4.
Conclusion
In this article, we discussed different control structures and loops in PHP. They are an essential part of PHP—or any programming language for that matter.
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