PHP Looping
Looping statements in
PHP are used to execute the same block of code a specified number of times.
Looping
Very often when you
write code, you want the same block of code to run a number of times. You can
use looping statements in your code to perform this.
In PHP we have the
following looping statements:
- 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
- for -
loops through a block of code a specified number of times
- foreach -
loops through a block of code for each element in an array
The while Statement
The while statement
will execute a block of code if and as long as a condition is true.
Syntax
while (condition)
code to be executed;
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Example
The following example
demonstrates a loop that will continue to run as long as the variable i is less
than, or equal to 5. i will increase by 1 each time the loop runs:
<html>
<body>
<?php
$i=1;
while($i<=5)
{
echo "The number is " . $i . "<br />";
$i++;
}
?>
</body>
</html>
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The do...while Statement
The do...while
statement will execute a block of code at least once - it then will
repeat the loop as long as a condition is true.
Syntax
do
{
code to be executed;
}
while (condition);
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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 5:
<html>
<body>
<?php
$i=0;
do
{
$i++;
echo "The number is " . $i . "<br />";
}
while ($i<5);
?>
</body>
</html>
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The for Statement
The for statement is
the most advanced of the loops in PHP.
In it's simplest form,
the for statement is used when you know how many times you want to execute a statement
or a list of statements.
Syntax
for (init; cond; incr)
{
code to be executed;
}
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Parameters:
- init: Is
mostly used to set a counter, but can be any code to be executed once at
the beginning of the loop statement.
- cond: Is
evaluated at beginning of each loop iteration. If the condition evaluates
to TRUE, the loop continues and the code executes. If it evaluates to
FALSE, the execution of the loop ends.
- incr: Is
mostly used to increment a counter, but can be any code to be executed at
the end of each loop.
Note: Each of the parameters can be
empty or have multiple expressions separated by commas.
- cond: All
expressions separated by a comma are evaluated but the result is taken
from the last part. This parameter being empty means the loop should be
run indefinitely. This is useful when using a conditional break statement
inside the loop for ending the loop.
Example
The following example
prints the text "Hello World!" five times:
<html>
<body>
<?php
for ($i=1; $i<=5; $i++)
{
echo "Hello World!<br />";
}
?>
</body>
</html>
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The foreach Statement
The foreach statement
is used to loop through arrays.
For every loop, the
value of the current array element is assigned to $value (and the array pointer
is moved by one) - so on the next loop, you'll be looking at the next element.
Syntax
foreach (array as value)
{
code to be executed;
}
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Example
The following example
demonstrates a loop that will print the values of the given array:
<html>
<body>
<?php
$arr=array("one", "two", "three");
foreach ($arr as $value)
{
echo "Value: " . $value . "<br />";
}
?>
</body>
</html>
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