Loops (while, for, foreach)

In many real-world applications, you often need to repeat a block of code multiple times — whether it’s displaying a list of users, processing data, or generating dynamic content. Writing the same code repeatedly is inefficient, and that’s where loops come in.

In this lesson, you’ll learn how to use loops in PHP, including while, for, foreach, and do...while. By the end, you’ll be able to efficiently repeat tasks and work with arrays in your applications.

What are Loops in PHP?

Loops allow you to execute a block of code multiple times based on a condition. Instead of writing repetitive code manually, you define a loop that runs until a condition is no longer true.

The while Loop

The while loop executes a block of code as long as a condition remains true.

Syntax

while (condition) {
    // code to execute
}

Example

$i = 1;

while ($i <= 5) {
    echo $i . " ";
    $i++;
}

Output:

1 2 3 4 5

Use case:

Use while when you don’t know in advance how many times the loop should run.

The do...while Loop

The do...while loop is similar to while, but it always executes the code at least once, even if the condition is false from the start.

Syntax

do {
    // code to execute
} while (condition);

Example

$i = 10;

do {
    echo $i;
    $i++;
} while ($i <= 5);

Output:

10

Use case:

Useful in scenarios like retry logic, menu-driven programs, or form handling where the code must run at least once.

The for Loop

The for loop is used when you know exactly how many times you want to run a block of code.

Syntax

for (initialization; condition; increment) {
    // code to execute
}

Example

for ($i = 1; $i <= 5; $i++) {
    echo $i . " ";
}

Output:

1 2 3 4 5

Use case:

Ideal for counting loops, such as iterating a fixed number of times.

The foreach Loop

The foreach loop is specifically designed for working with arrays. It allows you to loop through each element in an array easily.

Example

$colors = ["red", "blue", "green"];

foreach ($colors as $color) {
    echo $color . " ";
}

Output:

red blue green

Associative Array Example

$user = [
    "name" => "Rohan",
    "age" => 22
];

foreach ($user as $key => $value) {
    echo $key . ": " . $value . " ";
}

Output:

name: Rohan age: 22

Explanation:

In real applications, associative arrays are often used for data like database records, where keys represent column names such as name or age.

Use case:

Best for looping through arrays, especially when working with database results or structured data.

Key Differences: while vs for vs foreach

Loop Type | Best Use Case              | When to Use
--------- | -------------------------- | -----------------------------
while     | Unknown iterations         | Condition-based loops
for       | Fixed number of iterations | Counting loops
foreach   | Arrays                     | Looping through collections

Best Practice

Prefer foreach when working with arrays because it is more readable and less error-prone compared to manual indexing with for.

Common Mistakes Beginners Make

1. Infinite Loop (Missing Increment)

$i = 1;

while ($i <= 5) {
    echo $i;
}

Why it fails:

The loop never stops because $i is never updated.

Correct version:

$i = 1;

while ($i <= 5) {
    echo $i;
    $i++; // Fix
}

2. Wrong Loop Condition

for ($i = 1; $i >= 5; $i++) {

Why it fails:

The condition is incorrect, so the loop may never execute.

3. Modifying Array While Looping

foreach ($colors as $color) {
    $colors[] = "new";
}

Why it’s risky:

This can lead to unexpected behavior or infinite loops.

Real-World Example

$prices = [100, 200, 300];
$total = 0;

foreach ($prices as $price) {
    $total += $price;
}

echo "Total Price: ₹" . $total;

Output:

Total Price: ₹600

What this shows:

• Looping through array (foreach)
• Arithmetic operation (+=)
• Real-world use case (cart total calculation)

Practice Exercise

Task 1

Print numbers from 1 to 5 using a loop.

Expected Output:

1 2 3 4 5

Task 2

Loop through an array of 3 names and print them.

Expected Output:

Rohan Amit Rahul

Task 3

Calculate the sum of numbers in an array.

Expected Output:

600

Summary

In this lesson, you learned how loops work in PHP using while, for, foreach, and do...while. These loops allow you to repeat tasks efficiently and handle collections of data like arrays.

Mastering loops is essential for building dynamic applications such as dashboards, reports, and data-driven features.