Php exit from foreach. Nested for loop
In the case of nested loops, it may be necessary to leave not only the current nested loop, but the enclosing loop. In this case, you can get out of the situation due to additional variables: for (int i=0; i Not a very beautiful solution. That’s why such cases are an excuse for “goto”: for (int i=0; i This is shorter, more elegant, but.. .with "goto"! This is the same "goto" that caused many mental illnesses, bankruptcies and falls in the NASDAQ index. Couldn't it be just as brief, but without Dijkstra's favorite enemy, which we will talk about in the next article? Maybe in Are there better techniques in other languages?
Java
Java uses a named block technique to get rid of goto. LOOP: for(int i=0; i Although it would be much clearer like this: for(int i=0; i There is a strong suspicion that they didn’t do this only because it looks very much like a simple replacement keyword"goto" to "break".PHP
In PHP, breaking out of a nested loop looks, in my opinion, much more elegant. After “break”, the number of nested loops that the “break” operator must “leave” is indicated. In the above example, which is similar to the one above for Java, "break" must "cross" two braces")" to be outside of two loops. for($i=0; $i |
This improvement occurred to the author of these lines long before he became acquainted with PHP. This “parallel invention” confirms the impossibility of a complete monopoly on good ideas. But since there were ideas not only about “break N”, then when dating PHP I noticed that there is no “continue N” in it. An idea that is quite “symmetrical” to the previous one. Although it is not very easy to give a real-life example to illustrate its usefulness for the use of "continue N". Perhaps readers of these lines will suggest something in the comments to the article.
Bottom line
And so, now we need to present the findings in a systematized form in combination with our “symmetrical bracketed” style: (int i=0 loop i Replacing the keyword “break” with “exit”, as it seems, is more consistent with the meaning of the action being performed. But this is for those who prefer to program using English identifiers. For adherents of the widespread use of Russian speech, there is only one keyword - “exit". And now, of course, it would be interesting to know what graphic (instead of syntactic) sugar the IDE programmer should offer. It was It would be logical to see something like this:
It turns out very clearly. The arrows from the keyword “exit” indicate which loop will be exited from. If "exit" has a numeric operand, then the arrow must cross the boundaries of several cycles. The value of the operand is equal to the number of loops left. The “continue” statement is accompanied by another kind of arrow, the appearance of which reminds you of returning to the beginning of the loop.
Once again I would like to note that graphic design The above examples only illustrate the idea, but are neither the only nor the final option. Icons, arrows and other graphic elements can and will have a different appearance, but for now they show the very principle of text-graphic composition of program text.
Reviews
2013/05/07 16:37 , koba
Generally speaking, breaking out of a deeply nested loop outside of the outer loop is the only excuse for goto lovers. In reality, such amateurs do not understand, and their opponents do not show (maybe they do not understand either), one circumstance that shows their poor understanding of programming principles. Let's see what is the point of several nested loops, from which you have to exit from the innermost one? And the meaning is very simple: a certain set of absolutely equivalent elements is checked, but the programmer, for one reason or another, cut this set into several dimensions. That is, he presented certain elements as unequal, but at the same time wants to treat them as equal. Of course, such programmers not only cannot resolve this contradiction, but do not even know about its existence. That is, they replace scanning of the set as a whole with scanning of individual dimensions. Therefore, they have to use such an awkward technique as jumping out.
In fact, when the programmer realizes that he has turned equal elements into unequal elements, a solution immediately arises with one single loop - a pass through the entire set of equal elements.
It happened with goto and nested loops like this: int matrix[n][m];
int value;
...
for(int i=0; i
printf("value %d found in cell (%d,%d)\n",value,i,j);
goto end_loop;
}
printf("value %d not found\n",value);
end_loop: ; It became without goto and with one loop like this (example in C): int matrix[n][m];
int value;
...
int i = 0;
int j = 0;
int f;
while (!((f = (matrix[i][j] == value)) !! (i == n) && (j == m)))
if (!(j = ++j % m)) i = ++i % n;
if (f) printf("value %d found in cell (%d,%d)\n",value,i,j);
else printf("value %d not found\n",value);
Well, let's imagine that we have an array of links that we iterate through in an enclosing loop. The elements of this array refer to, say, some other arrays of unequal length. We will iterate through these arrays in the inner loop. Isn't that logical? And if we are faced with the task of searching, then having found the desired element, we boldly give the command “exit 2” and exit both cycles. A mediocre problem, a mediocre solution, but in the shortest possible way.
2014/01/31 10:40 , Pensulo
An example of solving the problem you proposed in VisualBasic using just one loop: Const iMax As Integer = 100
Private Source(1 To iMax) As Variant
" Source is a one-dimensional array consisting of links
" to other one-dimensional arrays of variable length.
Function SearchInArray(Required As String) As Boolean
i = 1: SearchInArray = False
Do
j = LBound(Source(i)) " Get starting index variable array
SearchInArray = True
Exit Do" in this example you can immediately use "Exit Function"
End If
j = j + 1
If j > UBound(Source(i)) Then
" Analyze going beyond the final index of a variable array
i = i + 1
End If
Loop Until i > iMax
End Function Similarly, this problem can be solved in any language without using the exit operator from the enclosing (outer) loop.
The solution with two cycles is given below. I would like to note that in this case, the exit operator from the enclosing (outer) loop was not required: Function SearchInArray2(Required As String) As Boolean
Dim i As Integer: Dim j As Integer
i = 1: SearchInArray2 = False
Do
j = LBound(Source(i))
Do
If Source(i)(j) = Required Then
SearchInArray2 = True
Exit Do "Again, in this example, you can immediately use "Exit Function"
End If
j = j + 1
Loop Until j > UBound(Source(i))
If SearchInArray2 = True Then
" This analysis can be omitted if the "Exit Function" was used earlier
Exit Do
End If
i = i + 1
Loop Until i > iMax
End Function
The example you provided uses additional variables to tell the outer loop whether to continue or not. Those. obviously a longer solution.
2014/02/25 15:49 , Ruslan
A shorter solution is not always better than a longer solution. In any case, the Feng Shui solution will be better.
2014/07/02 05:56 , utkin
It turns out very clearly. The arrows from the keyword “exit” indicate which loop will be exited from. If "exit" has a numeric operand, then the arrow must cross the boundaries of several cycles. The value of the operand is equal to the number of loops left. The “continue” statement is accompanied by another kind of arrow, the appearance of which reminds you of returning to the beginning of the loop.
For such a fragment, yes, it is very convenient. For full program it will be the brightest, wild vinaigrette, hurting the eyes with its variegation.
The IDE should have settings that enable or disable the display of certain graphic elements, for example: “accompany the exit statement with an arrow”, “accompany conditional statements with icons”, etc. Then everyone can customize it to their liking.
2014/11/07 11:30 , Sergey
2 koba Reducing the level of loop nesting (“flattening”) is a purely technical technique, which in this situation has only one goal - to avoid exiting a deeply nested loop. However, the result is achieved at the cost of loss of clarity and understandability of the code. Using "exit 2" in this situation does not have any harmful consequences, completely preserves the efficiency of the code and, most importantly, does not harm the ease of reading and understanding of the code.2014/11/27 09:06 , enburk
1
Even the goto option is instantly readable. You have to look at the corrected version and think about what the author intended...
I would also suggest writing “exit exit” instead of “exit 2”.
Also an option. But when traversing a multidimensional array in a loop, you will need to write “exit exit ... exit”.
2015/11/02 01:04 , Nick
2 Sergey+1
2 coba
but if it comes to that, then for C it was possible to write it simpler: int matrix[n][m];
int value;
int f;
for(int i = n * m; --i >= 0 && f = (matrix[i] != value););
if (!f) printf("value %d found in cell (%d,%d)\n",value,i,j);
else printf("value %d not found\n",value); And in general, all these continue, break, etc. just syntactic sugar.
continue is easily replaced by the if()() statement. break is not exactly sugar, of course, because an additional variable is needed for replacement, but if goto were not abused, then break would not be needed... (but “would” gets in the way)
P.S. Even this entry int matrix[n][m]; - syntactic sugar. But if you remove this sugar from languages, you will have assembler.
2D matrices are the easiest way to show the case where "goto" is useful because it's shorter. In the absence of other options, of course. But "break N" elegantly eliminates this probably the only reasonable use of "goto" - doesn't it? And to work with elements of sets, it is better to use the “foreach” loop.
2016/07/03 13:36 , rst256
No, that's not true, there's no need for goto? Just like you don't need an extra cycle, it's good correct option already demonstrated here.
And here is the first code with goto that came to hand: static size_t utf8_decode(const char *s, const char *e, unsigned *pch) (
unsigned ch;
If (s >= e) (
*pch = 0;
return 0;
}
Ch = (unsigned char)s;
if (ch< 0xC0) goto fallback;
if (ch< 0xE0) {
if (s+1 >= e !! (s & 0xC0) != 0x80)
goto fallback;
*pch = ((ch & 0x1F)<< 6) !
(s&0x3F);
return 2;
}
if (ch< 0xF0) {
if (s+2 >= e !! (s & 0xC0) != 0x80
!! (s & 0xC0) != 0x80)
goto fallback;
*pch = ((ch & 0x0F)<< 12) !
((s&0x3F)<< 6) !
(s&0x3F);
return 3;
}
{
unsigned res = 0;
goto fallback; /* invalid byte sequence, fallback */
res = (res<< 6) ! (cc & 0x3F); /* add lower 6 bits from cont. byte */
ch<<= 1; /* to test next bit */
}
if (count > 5)
goto fallback; /* invalid byte sequence */
res != ((ch & 0x7F)<< (count * 5)); /* add first byte */
*pch = res;
return count+1;
}
fallback:
*pch = ch;
return 1;
) If the fallback code seems small enough to you to spawn it instead of calling goto, then add a couple hundred more lines to it, it won’t change the essence
If (s >= e) (
*pch = 0;
return 0;
}
Ch = (unsigned char)s;
if (ch< 0xC0)
if (ch< 0xE0) {
if (s+1 >= e !! (s & 0xC0) != 0x80)
fallback(*pch, ch); return 1;
*pch = ((ch & 0x1F)<< 6) !
(s&0x3F);
return 2;
}
if (ch< 0xF0) {
if (s+2 >= e !! (s & 0xC0) != 0x80
!! (s & 0xC0) != 0x80)
fallback(*pch, ch); return 1;
*pch = ((ch & 0x0F)<< 12) !
((s&0x3F)<< 6) !
(s&0x3F);
return 3;
}
{
int count = 0; /* to count number of continuation bytes */
unsigned res = 0;
while ((ch & 0x40) != 0) ( /* still have continuation bytes? */
int cc = (unsigned char)s[++count];
if ((cc & 0xC0) != 0x80) /* not a continuation byte? */
fallback(*pch, ch); return 1;/* invalid byte sequence, fallback */
res = (res<< 6) ! (cc & 0x3F); /* add lower 6 bits from cont. byte */
ch<<= 1; /* to test next bit */
}
if (count > 5)
fallback(*pch, ch); return 1;/* invalid byte sequence */
res != ((ch & 0x7F)<< (count * 5)); /* add first byte */
*pch = res;
return count+1;
}
) It'll do? But if it were possible to return several values from a function, then “return 1, pch” would look more beautiful.
2016/08/10 18:55 , rst256
It'll do? But if it were possible to return several values from a function, then “return 1, pch” would look more beautiful.
Maybe yes. At least, that’s what I did when adapting this code for a lexer. You, too, as I understand it, fallback(*pch, ch) is a macro?
2017/09/19 13:27 , Comdiv
Many people have seen the title of Dijkstra's article, but few have read it. Dijkstra argues against non-sequential processes, and goto is just a violation method that was present in the languages of the time. Now they have created many specialized goto analogues for special cases, considering that they have solved the problem, but despite the fact that such limited gotos are better than a full-fledged goto, this does not fundamentally solve the problem. Where code correctness is critical, non-structural exits are not practiced. An example is MISRA C, which is the de facto standard for embedded systems in cars. In these requirements, non-structural jumps are prohibited almost completely, including premature return. An exception is made for the only break per cycle.
I asked Andrey Karpov, the developer of the static code analyzer PVS-Studio, how the “goto” operator, as well as “break”, “continue” and “return” affect the quality of the analyzer’s work. He answered in one word: “Bad.” True, it is not clear whether he attributed this only to “goto”, or to other operators as well. He promised to write an article on this topic, but somehow the inspiration doesn’t come to him...
2018/06/24 21:39 , rst256
The only thing that matters is how well we understand our code and how clearly we imagine its work in each of the possible situations. Apart from ourselves, no one can rid our code of errors and bugs: neither the strictest adherence to all the rules, nor the most ideal and reliable paradigm, nor the best and most advanced static analyzer.
No doubt, without a brain - nowhere. Yes, not simple, but burdened with relevant knowledge. But the brain can get tired, lose attentiveness, and cannot cope with the amount of information that must be kept in mind at the same time. And this is where auxiliary tools come to the rescue. You read about what errors a code analyzer finds, and you think: “No, in such a palisade of letters, numbers and symbols, I would look for an error until I turn gray.” Everything has its place: for the brain - creative work, for tools - routine. Well, the language should, if possible, warn against mistakes.
The for loop is one of the most commonly used loops in any programming language. In this article, we'll take a closer look at the PHP for loop.
For loop operator in PHP
A for loop in PHP executes a block of code a certain number of times based on a counter. In this case, the number of times that a block of code must be executed is determined in advance before entering the body of the loop.
for is one of the most complex types of loop. In PHP, a for loop behaves similarly to C. Below is the syntax structure:
for(expression1;expression2;expression3) statement;
In the above description, the for keyword indicates a loop. The parentheses define the expressions and then the statement to be executed.
How does a for loop work in PHP?
To understand how the for loop works, we need to understand these three expressions. Expression: expresison1 is the first one, which is executed only once before entering the loop. It is carried out unconditionally. This means that the expression will be executed the first time before entering the loop.
Expresison1 is called the initialization expression because it is used to initialize the counter that is used in expression2 and expression3 .
Expression2 ( condition check) is checked to determine whether the condition allows the instruction to be executed or not. The first time it runs after expression1 , then before entering the loop.
Typically expression2 contains a conditional statement to test whether the condition returns true or false . If the condition returns true, then the statement written in the loop will be executed.
Expression3 is executed at the end of each iteration after the loop statement. Typically programmers call it an increment expression. They use this expression to increment the value of a counter that was initialized in expression1 and evaluated in expression2 .
All three expressions are optional. You can also create a PHP loop like below:
for(;;) statement;
for(;expression2;expression3) statement;
If we have several lines in for loop, use curly braces as shown below:
for(expression1;expression2;expression3)( statement1; statement2; statement3; )
For Loop Flowchart
In the first step, expression1 is executed. If you look closely at the block diagram, you will find that there is no condition for expression1. expression1 is similar to the flow of the program being executed.
The next step executes expression2 immediately after expression1. It checks whether the loop condition is true. If the condition is true, then the loop will continue to execute, otherwise the thread will exit the loop.
If expression2 returns true, then the third step will execute the statement written in the for loop. After this, the third expression expression3 will be executed.
After expression3 is executed, the thread checks expression2 again, and the loop continues until expression2 returns false.
A simple example of a for loop in PHP
Let's consider the case when you need to display numbers from 1 to 10 separated by commas. Below is the code:
for($i=1;$i<=10;$i++) print $i.",";
Or with a curly brace:
for($i=1;$i<=10;$i++) { print $i.","; }
The expression $i=1 is expression1 , which is executed unconditionally. We use expression1 to initialize the variable to $i=1 .
Expression2 is the expression $i :
$i=1; for(;$i<=10;$i++) { print $i.","; }
$i=1; for(;$i<=10;) { print $i.","; $i++; }
Complex expression in a for loop
You can write three expressions in a for loop. We can write multiple statements in each expression in a for loop. Operators must be separated by commas.
Let's look at the example of the previous code to print a number from 1 to 10. Using multiple operators in an expression, you can write the code below:
for($i=1; $i<=10; print $i . ",", $i++);
Here expression3 is print $i.’,’, $i++ , which combines two operators, one is print $i. ‘,’ and the second one is $ i++ .
Above is an example where we have used multiple operators in expression3 . But you can also use multiple operators in any expression. For example:
Similarly, you can print all odd numbers less than 10 using the following code:
Array and for loop in PHP
You can use a PHP for loop to iterate through an array. For example, we have an array that contains the names of different people. We need to display all the names:
$names = array("Ankur", "John", "Joy"); $count = count($names); for($counter=0;$counter<$count;$counter++){ print $names[$counter]; }
You can also use a multidimensional array in a for loop:
$names = array(array("id" => 1, "name" => "Ankur"), array("id" => 2, "name" => "Joe"), array("id" => 3, "name" => "John"),); $count = count($names); for ($counter = 0; $counter< $count; $counter++) { print "Name".$names[$counter]["name"]." ID".$names[$counter]["id"]."n"; }
Nested for loop
It is possible to use a nested for loop in PHP. Example:
$metrix = array(array(1, 2, 3), array(2, 1, 3), array(3, 2, 1),); $count = count($metrix); for ($counter = 0; $counter< $count; $counter++) { $c_count = count($metrix[$counter]); for ($child = 0; $child < $c_count; $child++) { echo $metrix[$counter][$child]; } }
We have a multidimensional array and we use two PHP for loops to display the values of its elements.
When using a nested loop, you can use the parent for loop expression in the child loop. For example:
for ($i = 1; $i<= 5; $i++) {
for ($j = 1; $j <= $i; $j++) {
echo "*";
}
echo "
";
}
The above program is one of the most popular to print the * symbol in the shape of a right triangle.
Increment in a for loop
In almost every one of the examples above, we used expression3 , which is the last expression, as the increment instruction. We also often increased the value by one in all examples, for example $i++ or $j++ and so on. But we can increase the counter according to our requirements. For example, to print all odd numbers from 1 to 15, you could initialize the loop with the value 1 and iterate through 15, incrementing the counter by 2:
for($counter = 1; $counter<=15;$counter=$counter+2){ print $counter.","; }
The output of the above code will be " 1,3,5,7,9,11,13,15 " Here we increment the counter variable by +2 using the expression $counter=$counter+2 .
Exiting the for loop
You can break a loop under a certain condition using the break keyword. It is not part of a loop and is used to interrupt the execution of for , foreach , while , do-while and switch statements. Let's see how the break keyword stops a for loop.
A simple example where we print all the numbers in an array up to 100:
$series = array(1, 8, 5, 3, 100, 9, 7); for ($i = 0, $count = count($series); $i<= $count; $i++) { if (100 == $series[$i]) { break; } echo $series[$i] . " "; }
Here we break the loop by checking if the value of the array element is equal to 100.
You can also break a nested PHP loop through an array by passing the depth, for example, break 1 , break 2 and so on. See the example below:
for ($i = 0;; $i++) ( switch ($i) ( case 1: echo "This is one"; break 1; //This will only break the switch statement case 2: echo "This is two"; break 1 ; // This will again only break the switch statement case 3: echo "This is three "; break 2; // This will break both the switch and the for loop ) )
Here break 1 will break the switch statement, but break 2 will break the current statement as well as the parent one, i.e. both switch and for .
Using continue in a for loop
In the previous section, we learned how to break out of a loop. But what if you need to skip one iteration of the loop and go back to the loop? PHP has the continue keyword for this.
Let's recall an example of outputting odd numbers. All we did was start the loop at 1, increment the counter by 2, and print the result. Let's implement this example using continue :
for ($i = 0; $i< 20; $i++) { if ($i % 2 == 0) { continue; } echo $i . ","; }
In the above example, we check the expression $i%2 == 0 and if it is true, using the continue keyword, we skip the rest of the loop and return to expression3 ($i++) and then to expression2 ($i:
Sometimes you need to transfer data from a database table to an array using PHP:
10001, "name" => "Ankur", "country" => "India"), array("id" => 20002, "name" => "Joy", "country" => "USA"), array ("id" => 10003, "name" => "John", "country" => "UK"), array("id" => 20001, "name" => "Steve", "country" => "France"),); ?>
| ID | Name | Country | " . $table_data[$i]["id"] . " | " . "" . $table_data[$i]["name"] . " | " . "" . $table_data[$i]["country"] . " | " . ""; } ?>
|---|
The above code will generate the table.
Very often when writing scripts you need to perform the same action several times. This is what cycles are for. Loops in php, as in other languages, are divided into several types:
- Loop with a for counter
- Loop with while, do-while condition
- Loop to traverse arrays foreach
For example, when creating an online store, before displaying products on the screen, we need to remove products whose stock balance is below 10. To do this, we loop through the array with goods, and with the help conditional operator if, we check the number of products in the warehouse, and remove from the array all products whose value in the warehouse is less than 10.
For loop in PHP
Loop with a for counter- performed a certain number of times. Let's look at an example:
"; } ?>
In this example the loop will be executed 11 times. From 0 (since variable $i = 0) to 10 (since $i<= 10). Каждую итерацию $i будет увеличено на 1 ($i++). Чтобы было понятней, сделаем еще один пример:
"; } ?>
The loop will run from 5 to 9($i< 10 (в предыдущем примере было <= 10)).
The loop can also be executed in reverse order:
5; $i--) ( echo "Iteration number: $i
";
}
?>
The cycle will be executed from 10 to 5.
The cycle can also be executed with a certain step, let’s look at an example:
"; } ?>
The loop will perform 3 iterations (0, 5, 10) with a step of 5. Each iteration, the loop counter will be incremented by 5.
foreach loop in PHP
foreach loop- the most common cycle. Required in almost all scripts, especially if php script works with databases. Used to traverse arrays.
For example, let's look at a small example:
$value) ( echo "Key: $key, Value: $value
";
}
?>
When you run the script you will see:
Key: 0, Value: red Key: 1, Value: blue Key: 2, Value: green Key: color, Value: yellow Key: test, Value: design studio ox2.ru
While loop in PHP
while loop is used to execute a loop as long as a condition is met. If the condition is never met, the loop will go into a loop.
Let's look at an example:
"; } ?>
On the screen we will see numbers from 1 to 19
Do-while loop in PHP:
Cycle do-while- works exactly the same as while loop, the only difference is that the condition is satisfied after iteration. Let's write an example:
"; ) while ($i< 20); //Выполняем цикл до те пор, пока $i < 20 ?>
On the screen we will see numbers from 1 to 20. Please note that in the previous example with while loop was from 1 to 19, because the condition was satisfied before the loop iteration.
In order to break the cycle exists break function, she allows get out of the loop, no matter how many iterations are left until the end of the loop.
In order to skip an iteration and move on to the next iteration, there is continue function.
When creating websites, cycles are almost always used, regardless of the cost of creating the site, functionality and other things. So take them seriously!
Very often when writing scripts you need to perform the same action several times. This is what cycles are for. Loops in PHP, as in other languages, are divided into several types: Loop with a counter for Loop with a while, do-while condition Loop for traversing arrays foreach
OX2 2014-10-02 2014-10-02