#127 WIP adding examples of for loops

php-control-structures/notes/04-for-loop.md

@@ -1,3 +1,125 @@
-Notes coming soon.
+A for loop evaluates three expressions. 
 
-[Edit these notes](https://github.com/howToCodeWell/course-notes)
+On every iteration the second expression is re-evaluated until it resolves with a `false` outcome.
+
+Once the second expression has resolved `ture` loop is completed.
+
+The following is the structure of a PHP for loop
+```php
+for($expression1; $expression2; $expression3) {
+    // Run statement(s)
+}
+```
+The first expression is evaluated once at the beginning of the loop.
+
+The second expression is evaluated per iteration. If the second expression resolves `true` then the statement(s) within the body of the for loop are executed.
+
+If the second expression resolved `false` then the execution of the loop ends.
+
+At the end of each iteration the third expression is evaluated.
+
+The following is a real world example of how to use a for loop. 
+
+In this example the `$discount` increases by `5` for every iteration of the loop.
+
+
+```php
+$discount = 0;
+$productLimit = 3;
+for ($basketQty = 1; $basketQty <= $productLimit; $basketQty++) {
+    $discount = $discount + 5;
+    echo 'Basket QTY is now '. $basketQty . "\n";
+    echo 'Discount is now '. $discount . "\n";
+}
+
+// Basket QTY is now 1
+// Discount is now 5
+// Basket QTY is now 2
+// Discount is now 10
+// Basket QTY is now 3
+// Discount is now 15
+```
+
+# Breaking the loop
+
+When the conditional break statement is reached the loop no longer continues.
+
+```php
+for ($expression1; $expression2; $expression3) {
+    if ($expression1 === 2) {
+        break;
+    }
+}
+```
+In the below example the loop is broken when the `$discount` reaches the `$discountLimit`.
+```php
+
+$discount = 0;
+$discountLimit = 20;
+$productLimit = 10;
+
+for ($basketQty = 1; $basketQty <= $productLimit; $basketQty++) {
+    if ($discount === $discountLimit) {
+        echo 'Discount limit reached' . "\n";
+        break;
+    }
+    $discount = $discount + 5;
+    echo 'Basket QTY is now '. $basketQty . "\n";
+    echo 'Discount is now '. $discount . "\n";
+}
+
+// Basket QTY is now 1
+// Discount is now 5
+// Basket QTY is now 2
+// Discount is now 10
+// Basket QTY is now 3
+// Discount is now 15
+// Basket QTY is now 4
+// Discount is now 20
+// Discount limit reached
+```
+
+
+```php
+$productsInBasket = [
+    1, 1, 1, 1, 1, 1, 12, 15
+];
+$discount = 0;
+$discountLimit = 20;
+$productLimit = 10;
+$productIDWithDiscount = 1;
+$productLimit = 10;
+
+for ($productIndex = 0; $productIndex <= $productLimit; $productIndex++) {
+
+    if (!isset($productsInBasket[$productIndex])) {
+        echo 'Product at index ' . $productIndex . ' Not found .... Loop completed '. "\n";
+        break;
+    }
+
+    $currentProductID = $productsInBasket[$productIndex];
+
+    if ($discount === $discountLimit) {
+        echo 'Discount limit reached' . "\n";
+        continue;
+    }
+
+    if ($productIDWithDiscount === $currentProductID) {
+        $discount = $discount + 5;
+    }    
+
+    echo 'Discount is now '. $discount . "\n";
+}
+
+// Discount is now 5
+// Discount is now 10
+// Discount is now 15
+Discount is now 20
+Discount limit reached
+Discount limit reached
+Discount limit reached
+Discount limit reached
+Product at index 8 Not found .... Loop completed 
+
+
+```