Xtreme Coder

FOR is used in PHP to execute the same code a set number of times. The basic syntax of FOR is as follows:
FOR (expression 1, expression 2, expression 3)
{
  [code to execute]
}
FOR tells PHP to first execute "expression 1", then evaluate "expression 2". If "expression 2" is true, then [code to execute] is executed. After this, expression 3 is executed, and then "expression 2" is evaluated again. If "expression 2" is true, then [code to execute] is executed for a second time. The cycle continues until "expression 2" is no longer true.
Let's look at an example. Assuming we have the following piece of code:

FOR ($i = 0; $i <= 2; $i++) {   print "value is now " . $i . "<br>"; }

The output of the above code is:

value is now 0 value is now 1 value is now 2

During the 1st iteration, $i = 0, which means the expression, ($i <= 2), is true. Therefore, the print statement is executed, and $i gets incremented by 1 and becomes 1.
During the 2nd iteration, $i = 1, which means the expression, ($i <= 2), is true. Therefore, the print statement is executed, and $i gets incremented by 1 and becomes 2.
During the 3rd iteration, $i = 2, which means the expression, ($i <= 2), is true. Therefore, the print statement is executed, and $i gets incremented by 1 and becomes 3.
During the 4th iteration, $i = 3, which means the expression, ($i <= 2), is false. Therefore, PHP exits out of the FOR loop, and does not execute the print statement.


DO .. WHILE is used in PHP to provide a control condition. The idea is to execute a piece of code while a condition is true. The basic syntax of DO .. WHILE is as follows:
DO {
  [code to execute]
} WHILE (conditional statement)
The difference between DO .. WHILE and WHILE is that DO .. WHILE will always execute the [code to execute] at least once, and in a WHILE construct, it is possible for the [code to execute] to never execute.
Let's look at an example. Assuming we have the following piece of code:

$i = 5 DO {   print "value is now " . $i . "<br>";   $i--; } WHILE ($i > 3);

The output of the above code is:

value is now 5 value is now 4

During the 1st iteration, $i = 5, the print statement is executed, $i gets decreased by 1 and becomes 4, then PHP checks the expression, ($i > 3), which turns out to be true. Therefore, the loop continues.
During the 2nd iteration, $i = 4, the print statement is executed, $i gets decreased by 1 and becomes 3, then PHP checks the expression, ($i > 3), which is no longer true. Therefore, PHP exits the loop.
If we change the above code to:

$i = 0 DO {   print "value is now " . $i . "<br>";   $i--; } WHILE ($i > 3);

The output would then be:

value is now 0

Even though the expression ($i > 3) is false from the very beginning, one line is still printed out because in DO .. WHILE, the code in the bracket following DO is always executed at least once.

FOREACH is used in PHP to loop over all elements of an array. The basic syntax of FOREACH is as follows:
FOREACH ($array_variable as $value)
{
  [code to execute]
}
or
FOREACH ($array_variable as $key => $value)
{
  [code to execute]
}
In both cases, the number of times [code to execute] will be executed is equal to the number of elements in the $array_variable array.
Let's look at an example. Assuming we have the following piece of code:

$array1 = array(1,2,3,4,5); FOREACH ($array1 as $abc) {   print "new value is " . $abc*10 . "<br>"; }

The output of the above code is:

new value is 10 new value is 20 new value is 30 new value is 40 new value is 50

The FOREACH loop above went through all 5 elements of array $array1, and each time prints out a statement containing 10x the array element value.


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