Loops¶

Loops allow a script to repeat an action multiple times. Each loop type has a specific purpose and syntax. This section explains how each loop works, how the syntax is structured, and provides examples that students can run directly on their machines.

1. for Loop¶

The for loop is used when you know exactly how many times you want to repeat something.

Its syntax mirrors C‑style loops:

for (<initialization>; <condition>; <iteration>) {
    <code>
}

• initialization: runs once before the loop starts
• condition: checked before each iteration
• iteration: runs after each iteration

Example: counting from 1 to 5¶

for ($i = 1; $i -le 5; $i++) {
    "Iteration: $i"
}

Explanation:

• $i = 1 sets the starting value.
• $i -le 5 keeps the loop running while $i is 1 through 5.
• $i++ increases $i by 1 each time.
• The loop prints:

Iteration: 1
Iteration: 2
Iteration: 3
Iteration: 4
Iteration: 5

Example: summing numbers¶

$sum = 0

for ($i = 1; $i -le 5; $i++) {
    $sum += $i
}

$sum

This calculates 1 + 2 + 3 + 4 + 5 and prints 15.

2. foreach Loop¶

foreach is used to iterate through each element in a collection (arrays, lists, command output).

Syntax:

foreach (<item> in <collection>) {
    <code>
}

Example: iterating through an array¶

$colors = "red", "green", "blue"

foreach ($color in $colors) {
    "Color: $color"
}

Explanation:

• $colors contains three strings.
• On each iteration, $color holds one element.
• The loop prints each color.

Example: processing files¶

$files = Get-ChildItem

foreach ($file in $files) {
    $file.Name
}

Explanation:

• Get-ChildItem returns an array of file objects.
• $file.Name prints the name of each file.

3. while Loop¶

while repeats as long as a condition remains true.

Syntax:

while (<condition>) {
    <code>
}

The condition is checked before each iteration.

Example: count down from 5¶

$i = 5

while ($i -gt 0) {
    "Countdown: $i"
    $i--
}

Explanation:

• $i starts at 5.
• The loop runs while $i is greater than 0.
• $i-- decreases the value each time.

Example: waiting for a condition¶

$number = 0

while ($number -lt 3) {
    "Number is $number"
    $number++
}

This prints:

Number is 0
Number is 1
Number is 2

4. do Loop¶

A do loop always runs at least once, because the condition is checked after the loop body.

There are two forms:

• do { } while (<condition>)
• do { } until (<condition>)

4.1 do … while¶

Runs the block, then repeats while the condition is true.

Example¶

$i = 1

do {
    "Value: $i"
    $i++
} while ($i -le 3)

Explanation:

• The loop prints values 1, 2, and 3.
• The condition is checked after each iteration.

4.2 do … until¶

Runs the block until the condition becomes true.

Example¶

$i = 1

do {
    "Value: $i"
    $i++
} until ($i -gt 3)

Explanation:

• The loop runs until $i becomes greater than 3.
• It prints the same output as the previous example.

5. Choosing the Right Loop¶