Detailed explanation of several loops in php while, for, foreach, do while

Loop structure
1. while loop

while(
表达式
)
 {
  循环体;//反复执行，直到表达式为假
 }

Code:

$index = 1;
while ($index<5)
{
      print "Number is {$index}
";
     $index++;
}
print "Done";

Run Result:
Number is 1
Number is 2
Number is 3
Number is 4
Done

2. do while loop

do {
      循环体;//反复执行，直到表达式为假
} while(表达式)

Code:

do {
         $index++;
         print "Number is {$index}
";
} while($index<0);
print "Done";

Run result:
Number is 1
Done

There is a certain difference between the Do While loop statement and while. The difference between them is that do while will be executed first regardless of whether the condition is true, while while will only be executed once if it is true.

三, for loop
According to different loop conditions, there are two types of loops
One: counting loop (generally use for)
The other: conditional loop ( Generally use while do-while)

for (expr1; expr2; expr3) {
   statement
 }

where expr1 is the initial value of the condition. expr2 is the condition for judgment, usually using logical operators (logical operators)
The conditions for judgment. expr3 is the part to be executed after statement is executed. It is used to change the conditions for the next loop judgment, such as adding one, etc. And statement
is the execution part of the program that meets the conditions. If the program has only one line, the curly brackets {} can be omitted.
The following example is an example of "I won't dare to do it again" written using a for loop. It can be compared with the one using a while loop.

<?php
 for ($i=1; $i<=10; $i++) {
   echo "$i. 以后不敢了n";
 }
?>

Run results:
1. I won’t dare anymore
2. I won’t dare anymore
3. I won’t dare anymore
4. I won’t dare anymore I dare
5. I won’t dare anymore
6. I won’t dare anymore
7. I won’t dare anymore
8. I won’t dare anymore
9. I won’t dare anymore
10. I won’t dare anymore
4. Foreach loop
The foreach statement is used to looptraverse the array. Each time the loop is performed, the value of the current array element will be assigned to the value variable (the array pointer will move one by one) - and so on
Syntax:

foreach (array as value)
{
    code to be executed;
}

Code:

<?php
$arr=array("one", "two", "three");
foreach ($arr as $value)
{
  echo "Value: " . $value . "
";
}
?>

Running results:
Value: one
Value: two
Value: three
The above are four loop bodies in PHP, selected according to different conditions The corresponding loop body uses

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