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;
}
|
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:
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:
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
An array is a data structure that stores one or more similar type of
values in a single value. For example if you want to store 100 numbers
then instead of defining 100 variables its easy to define an array of
100 length.
There are three different kind of arrays and each array value is accessed using an ID c which is called array index.
- Numeric array - An array with a numeric index. Values are stored and accessed in linear fashion
- Associative array - An array with strings as index. This
stores element values in association with key values rather than in a
strict linear index order.
- Multidimensional array - An array containing one or more arrays and values are accessed using multiple indices
NOTE: Built-in array functions is given in function reference
PHP Array Functions
Numeric Array
These arrays can store numbers, strings and any object but their
index will be prepresented by numbers. By default array index starts
from zero.
Example
Following is the example showing how to create and access numeric arrays.
Here we have used
array() function to create array. This function is explained in function reference.
<html>
<body>
<?php
/* First method to create array. */
$numbers = array( 1, 2, 3, 4, 5);
foreach( $numbers as $value )
{
echo "Value is $value <br />";
}
/* Second method to create array. */
$numbers[0] = "one";
$numbers[1] = "two";
$numbers[2] = "three";
$numbers[3] = "four";
$numbers[4] = "five";
foreach( $numbers 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
Value is one
Value is two
Value is three
Value is four
Value is five
|
Associative Arrays
The associative arrays are very similar to numeric arrays in term of
functionality but they are different in terms of their index.
Associative array will have their index as string so that you can
establish a strong association between key and values.
To store the salaries of employees in an array, a numerically
indexed array would not be the best choice. Instead, we could use the
employees names as the keys in our associative array, and the value
would be their respective salary.
NOTE: Don't keep associative array inside double quote while printing otheriwse it would not return any value.
Example
<html>
<body>
<?php
/* First method to associate create array. */
$salaries = array(
"mohammad" => 2000,
"qadir" => 1000,
"zara" => 500
);
echo "Salary of mohammad is ". $salaries['mohammad'] . "<br />";
echo "Salary of qadir is ". $salaries['qadir']. "<br />";
echo "Salary of zara is ". $salaries['zara']. "<br />";
/* Second method to create array. */
$salaries['mohammad'] = "high";
$salaries['qadir'] = "medium";
$salaries['zara'] = "low";
echo "Salary of mohammad is ". $salaries['mohammad'] . "<br />";
echo "Salary of qadir is ". $salaries['qadir']. "<br />";
echo "Salary of zara is ". $salaries['zara']. "<br />";
?>
</body>
</html>
|
This will produce following result:
Salary of mohammad is 2000
Salary of qadir is 1000
Salary of zara is 500
Salary of mohammad is high
Salary of qadir is medium
Salary of zara is low
|
Multidimensional Arrays
A multi-dimensional array each element in the main array can also be
an array. And each element in the sub-array can be an array, and so on.
Values in the multi-dimensional array are accessed using multiple index.
Example
In this example we create a two dimensional array to store marks of three students in three subjects:
This example is an associative array, you can create numeric array in the same fashion.
<html>
<body>
<?php
$marks = array(
"mohammad" => array
(
"physics" => 35,
"maths" => 30,
"chemistry" => 39
),
"qadir" => array
(
"physics" => 30,
"maths" => 32,
"chemistry" => 29
),
"zara" => array
(
"physics" => 31,
"maths" => 22,
"chemistry" => 39
)
);
/* Accessing multi-dimensional array values */
echo "Marks for mohammad in physics : " ;
echo $marks['mohammad']['physics'] . "<br />";
echo "Marks for qadir in maths : ";
echo $marks['qadir']['maths'] . "<br />";
echo "Marks for zara in chemistry : " ;
echo $marks['zara']['chemistry'] . "<br />";
?>
</body>
</html>
|
This will produce following result:
Marks for mohammad in physics : 35
Marks for qadir in maths : 32
Marks for zara in chemistry : 39
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