PHP basic loop control statement study notes-PHP Tutorial-php.cn

PHP basic loop control statement study notes

伊谢尔伦

Release： 2023-03-11 06:22:02

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Conditional control statement, you can choose to execute different statements based on conditions. But sometimes you need to reuse a certain piece of code or function.

while loopStatement

While loop is the simplest loop statement in PHP. Its syntax format is:

while(expr){
     statement;
}

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whenExpressionWhen the value of expr is true, the statement statement will be executed. After the execution is completed, it will return to the expr expression to continue judgment. Until the value of the expression is false, the loop is broken out and the following statement is executed.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312"/>
<title>PHP语言基础</title>
</head>
<body>
<?php
header("Content-Type:text/html;   charset=gb2312");
$num=1;
$str="10以内的偶数为:";
while($num <= 10){
     if($num % 2 == 0){
          $str.=$num." ";
     }
     $num++;
}
echo $str;

?>
</body>
</html>

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Running results:
Even numbers within 10 are: 2 4 6 8 10

do...while loop statement

There is another form of while statement means, that is, do...while. The difference between the two is that do...while loops one more time than the while statement. When the value of the while expression is false, the while loop jumps out of the current loop directly; while the do...while statement executes the program block first and then judges the conditional expression.

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312"/>
<title>PHP语言基础</title>
</head>
<body>
<?php
header("Content-Type:text/html;   charset=gb2312");
$num=1;
while($num != 1){
     echo "不会看到";
}

do{
     echo "会看到";
}while($num != 1);

?>
</body>
</html>

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Running results:
You will see

for loopStatement

The for loop is the most complex loop structure in PHP. The syntax format is:

for(expr1;expr2;expr3){
   statement;
}

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Among them, expr1 takes a value unconditionally during the first loop; expr2 is evaluated before the start of each loop. If the value is true, the statement is executed, otherwise, jump out of the loop and continue. executed; expr3 is executed after each loop.

<!DOCTYPE html>
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312"/>
<title>PHP语言基础</title>
</head>
<body>
<?php
header("Content-Type:text/html;   charset=gb2312");
$num=1;
for($i=1;$i <= 100;$i++){
     $num*=$i;
}
echo "100!=".$num;
?>
</body>
</html>

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Run result:
100!=9.3326215443944E+157

foreach loop statement

The foreach loop was introduced in PHP4 and can only be used for arrays. In PHP5, support for objects has been added. Syntax format:

foreach(array_expression as $value)
     statement;

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foreach(array_expression as $key => $value)
     statenment;

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<!DOCTYPE html >
<html>
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312"/>
<title>PHP语言基础</title>
</head>
<body>
<?php
header("Content-Type:text/html;   charset=gb2312");
$name=array("1"=>"Jack","2"=>"Ben","3"=>"Bill");
foreach($name as $key => $value){
     echo " ".$name[$key];
}
?>
</body>
</html>

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Running result:
Jack Ben Bill

Another writing format for process control

In a complex PHP page, it may contain multiple conditional control statements, loop control statements and functions. It is very troublesome to just find matching braces "{}". For this purpose, PHP provides another writing format, including if, while, for, foreach and switch. The basic form of writing format is: use colon ":" to replace the left brace "{"; use endif;, endwhile, endfor, endforeach; and endswitch; to replace the right brace "}".

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=gb2312"/>
<title>PHP语言基础</title>
</head>
<body>
<?php
header("Content-Type:text/html;   charset=gb2312");
$ss=2;
$max=1000;
$arr=array();
echo $max."以内的素数为：";
while($ss < $max):
     $boo=false;
     foreach($arr as $value):
          if($ss % $value ==0):
               $boo=true;
               break;
          endif;
     endforeach;
     if(!$boo):
          echo $ss." ";
          $arr[count($arr)]=$ss;
     endif;
     $ss++;
endwhile;
?>

</body>
</html>

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Operation results:
The prime numbers within 1000 are: 2 3 5 7 11 13 17 19 23 29 31 37 41 43 47 53 59 61 67 71 73 79 83 89 97 101 103 107 109 113 127 131 137 139 149 151 157 163 167 173 179 181 191 193 197 199 211 223 227 229 233 239 241 251 257 263 269 271 277 281 283 29 3 307 311 313 317 331 337 347 349 353 359 367 373 379 383 389 397 401 409 419 421 431 433 439 443 449 457 461 463 467 479 487 491 499 503 509 521 523 541 547 557 563 569 571 577 587 593 599 601 607 61 3 617 619 631 641 643 647 653 659 661 673 677 683 691 701 709 719 727 733 739 743 751 757 761 769 773 787 797 809 811 821 823 827 829 839 853 857 859 863 877 881 883 887 907 911 919 929 937 941 947 95 3 967 971 977 983 991 997

Use break/continue Statement to jump out of the loop

When using a loop statement, sometimes the number of loops is uncertain. In this case, you can use an infinite loop, such as:

while(true){     ...}

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for(;;){     ...}

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Only when the program block meets certain conditions will it break out of the loop. The keywords used to break out of the loop are break and continue.

The break keyword can terminate the current loop, including all control statements including while, do...while, for, foreach and switch.
The break statement can not only jump out of the current loop, but also specify how many levels of loops to jump out of. The format is:

break $num;

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Parameter $num specifies how many levels of loops to jump out of.

The continue keyword is not as powerful as break. Continue can only terminate this loop and enter the next loop. Continue can also specify how many loops to jump out of.

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