Loops in PHP

Understand all loop types in PHP — for, while, do-while, and foreach — and learn how to use break and continue to control iteration.

for Loop

The `for` loop is ideal when you know in advance how many times to iterate. It bundles the initializer, condition, and increment into one concise header.

1. Basic for Loop

`for (init; condition; increment)` — runs while condition is true.

2. Counting Down

Decrement `$i` to iterate in reverse.

3. Custom Step

Increment by any amount using compound assignment.

4. Nested for Loops

Use nested loops for 2D iteration like tables or matrices.

while Loop

The `while` loop checks its condition before each iteration. Use it when the number of iterations is not known in advance — for example, reading lines from a file or polling until a result is ready.

1. Basic while

Loop runs while the condition is truthy.

2. Condition-driven while

Drive the loop with a changing condition, not just a counter.

3. while with Array Consumption

Use while to process items until a collection is empty.

do-while Loop

The `do-while` loop executes its body first, then checks the condition. This guarantees the body runs at least once — regardless of whether the condition is initially true.

1. Basic do-while

Body executes before the condition is checked.

2. Runs Once Even When Condition is False

Unlike `while`, `do-while` always executes the body at least once.

3. Menu / Retry Pattern

do-while is natural for "prompt once, repeat if needed" patterns.

foreach Loop

The `foreach` loop is PHP's most-used loop for iterating over arrays and objects. It automatically handles the index/key and value for each element.

1. foreach on Indexed Array

Iterate over values of an indexed array.

2. foreach with Key => Value

Access both key and value in an associative array.

3. Modifying Values with Reference (&)

Use `&$value` to modify array elements in place.

4. Nested foreach (Multidimensional Array)

Loop over nested arrays with nested foreach.

break & continue

PHP provides two keywords to alter loop execution: `break` exits the loop entirely, and `continue` skips the rest of the current iteration and moves to the next one.

1. break — Exit the Loop

Stop a loop immediately when a condition is met.

2. continue — Skip an Iteration

Jump to the next iteration without finishing the current one.

3. break with a Level Argument

Pass an integer to `break` to exit multiple nested loops at once.

4. break in foreach (Early Exit Search)

Use break to stop a search once a result is found.

Loop Guard Clauses

A guard clause inside a loop uses `continue` to reject invalid or unwanted items early, keeping the main logic flat and readable instead of nested inside an `if` block.

1. Guard Clause using continue

Skip invalid items at the top of the loop body.

2. Guard Clause with Multiple Conditions

Combine multiple guards at the top to filter out bad data.

Loop Best Practices

Small choices in how you write loops — like avoiding recalculating values in loop headers or choosing foreach over for for arrays — can meaningfully improve clarity and performance.

1. Cache count() Outside the Loop

Calling `count()` inside a loop header re-evaluates it every iteration.

2. Prefer foreach for Arrays

Use foreach instead of for when iterating over arrays.

3. Avoid Modifying an Array While Iterating

Modifying the array inside a foreach can produce unexpected behavior.