PHP Loop
Loops in PHP are used to
execute the same block of code a specified number of times. PHP supports
following four loop types.
- for - loops through a block of code a specified number of times.
- 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.
- foreach - loops through a block of code for each element in an array.
We will discuss about continue and break keywords used to control the loops
execution.
The for loop statement
The for statement is used when
you know how many times you want to execute a statement or a block of
statements.
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Syntax
for (initialization; condition; increment)
{
code to be executed;
}
|
The initializer is used to set
the start value for the counter of the number of loop iterations. A variable
may be declared here for this purpose and it is traditional to name it $i.
Example
The following example makes
five iterations and changes the assigned value of two variables on each pass of
the loop:
<html>
<body>
<?php
$a = 0;
$b = 0;
for( $i=0; $i<5; $i++ )
{
$a += 10;
$b += 5;
}
echo ("At the end of the loop a=$a and b=$b" );
?>
</body>
</html>
|
This will produce following
result:
At the end of the loop a=50 and b=25
|
The while loop statement
The while statement will
execute a block of code if and as long as a test expression is true.
If the test expression is true
then the code block will be executed. After the code has executed the test
expression will again be evaluated and the loop will continue until the test
expression is found to be false.
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Syntax
while (condition)
{
code to be executed;
}
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Example
This example decrements a
variable value on each iteration of the loop and the counter increments until
it reaches 10 when the evaluation is false and the loop ends.
<html>
<body>
<?php
$i = 0;
$num = 50;
while( $i < 10)
{
$num--;
$i++;
}
echo ("Loop stopped at i = $i and num = $num" );
?>
</body>
</html>
|
This will produce following
result:
Loop stopped at i = 10 and num = 40
|
The do...while loop 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.
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Syntax
do
{
code to be executed;
}while (condition);
|
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 10:
<html>
<body>
<?php
$i = 0;
$num = 0;
do
{
$i++;
}while( $i < 10 );
echo ("Loop stopped at i = $i" );
?>
</body>
</html>
|
This will produce following
result:
Loop stopped at i = 10
|
The foreach loop statement
The foreach statement is used
to loop through arrays. For each pass the value of the current array element is
assigned to $value and the array pointer is moved by one and in the next pass
next element will be processed.
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Syntax
foreach (array as value)
{
code to be executed;
}
|
Example
Try out following example to
list out the values of an array.
<html>
<body>
<?php
$array = array( 1, 2, 3, 4, 5);
foreach( $array as $value )
{
echo "Value is $value <br />";
}
?>
</body>
</html>
|
This will produce following
result:
Value is 1
Value is 2
Value is 3
Value is 4
Value is 5
|
The break statement
The PHP break keyword is used to terminate the
execution of a loop prematurely.
The break statement is situated inside the
statement block. If gives you full control and whenever you want to exit from
the loop you can come out. After coming out of a loop immediate statement to
the loop will be executed.
Example
In the following example
condition test becomes true when the counter value reaches 3 and loop
terminates.
<html>
<body>
<?php
$i = 0;
while( $i < 10)
{
$i++;
if( $i == 3 )break;
}
echo ("Loop stopped at i = $i" );
?>
</body>
</html>
|
This will produce following
result:
Loop stopped at i = 3
|
The continue statement
The PHP continue keyword is used to halt the current
iteration of a loop but it does not terminate the loop.
Just like the break statement the continue statement is situated inside the
statement block containing the code that the loop executes, preceded by a
conditional test. For the pass encountering continue statement, rest of the loop code is
skipped and next pass starts.
Example
In the following example loop
prints the value of array but for which condition becomes true it just skip the
code and next value is printed.
<html>
<body>
<?php
$array = array( 1, 2, 3, 4, 5);
foreach( $array as $value )
{
if( $value == 3 )continue;
echo "Value is $value <br />";
}
?>
</body>
</html>
|
This will produce following
result
Value is 1
Value is 2
Value is 4
Value is 5
|
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