Introduction to PHP loop function usage tutorial

The loop in PHP main user executes the same code block run specified times.

There are four main types of PHP loops: while, do…while, for, foreach. Below we will explain the usage of each cycle separately.

While statement:

As long as the specified condition is true, the code block is executed loop.

Format:

while(expr)
{
statement;
}

Semantics: First, judge expr, if the expression expr is false, it ends; if the expression expr is true, execute the statement statement, and judge expr again after the execution. If the expression expr is still true, continue to execute the statement statement until the expression expr is false, end.
example:

Copy the codeThe code is as follows:

 
<?php
$i=1;
while($i<=5){
echo $i;
$i++;
}
?>

The above example shows a loop, and the code will continue to execute as long as the variable i is less than or equal to 5. Every time the loop is cycled, the variable will be incremented by 1, and then the value of i is entered;

do…while statement:

First execute the code block once, and then repeat the loop when the specified condition is true.
Format:

do{
statement;
}

while(expr) semantics: first execute the statement statement once, then judge expr, if the expression expr is false, it ends; if the expression expr is true, continue to loop the statement statement, and judge expr again after the execution. If the expression expr is still true, continue to execute the statement statement until the expression expr is false, end.

Note: The difference between him and while is that do...while executes a statement once without making any judgments for the first time, and then determines whether the conditions are true. Here you should note that others are the same as while.
example:

Copy the codeThe code is as follows:

<?php 
$i=6;
do
  {
  $i++;
  echo "The number is " . $i . "<br />";
  }
while ($i<5);
?>

The above example shows a loop. I assign a value of 6 to the variable i. It is obvious that it is not true here compared to the conditions in while. However, the result is input 6, which is the do...while statement mentioned earlier. It did not make any judgment for the first time, and then execute it once, and then determine whether the conditions are true.

for statement

:If you have determined the number of repetitions of a code block, you can use the for statement.
grammar

for (initialization; condition; increment)
{
code to be executed;
}

Semantics: The for statement has three parameters. The first parameter initializes the variable, the second parameter holds the condition, and the third parameter contains the increments required to execute the loop. If multiple variables are included in the initialization or increment parameters, they need to be separated by commas. The condition must be calculated as true or false.
example:

The following example will display the text "Hello World!" 5 times:

Copy the codeThe code is as follows:

<?php
for ($i=1; $i<=5; $i++)
{
  echo "Hello World!<br />";
}
?>

foreach statement: The foreach statement is used to loop through an array.

Each time a loop is performed, the value of the current array element is assigned to the value variable (the array pointer will move one by one) - and so on.
grammar

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

example
The following example illustrates a loop that outputs the value of a given array:

Copy the codeThe code is as follows:

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

Definition: First I define an array arr, and then I use foreach to loop, where ($arr as $value) means, assign the value in the $arr array to $value, and then execute the statement to output the value of $value.
The output result is:

one
two
three