Iteration in Practice

Let’s put iteration into practice. In this episode, you will learn about the different iterator constructs in each language. Then you’ll see them in action.

Your key takeaways are:

• for, each, foreach instructions provide iterations through arrays, collections, or objects
• while, do/while, until instructions provide looping until the conditional expression is false

Study Notes

Types of Iterators

There are several types of iterators:

• for loop
• foreach
• do/while
• while
• each

Iterators for each language:

Language	for	foreach, each	do/while, while, until
PHP	Yes	Yes	Yes
JavaScript	Yes	Yes	Yes
Ruby	Yes	Yes	Yes
Python	Yes		Yes
C	Yes		Yes
C#	Yes	Yes	Yes
Visual Basic	Yes	Yes	Yes

For Loop

In the following code:
for ( counter = 0; counter < 10; counter++ ) {}

This is how it breaks down:

• for: instruction keyword
• counter = 0: “counter” is the variable that holds the number of loops, statement initializes the variable
• counter < 10: test if counter is within the threshold, threshold (limit)
• counter++: increment the counter

Foreach Loop

In the following code:

foreach ( variable as key => value ) {}

This is how it breaks down:

• foreach: instruction keyword
• variable: represents the collection
• key: current key
• value: current value

JavaScript Foreach/Each Loop

In the following code:

for ( variable of object ) {}

This is how it breaks down:

• for: instruction keyword
• variable: current value
• object: represents the collection

In the following code:

variable.forEach(function ( value, key ) {});

This is how it breaks down:

• variable: represents the collection
• forEach: instruction keyword
• value: current value
• key: current key (index)

While Loop

In the following code:

while ( condition ) {}

This is how it breaks down:

• while: instruction keyword
• condition: conditional expression

The while loop will iterate as long as the condition is true.

Do/While Loop

In the following code:

This is how it breaks down:

• do and while: instruction keyword
• condition: conditional expression

Unlike the while loop, the do/while will do the work within the code block at least once, regardless of the conditional in the while. Why? Because the conditional is checked after the code block.