124 conditional statements

php-control-structures/notes/01-conditional-statements.md

@@ -0,0 +1,95 @@
+A conditional statement changes the flow of the application based on the evaluation of a condition.
+
+There are three types of conditional statements in PHP
+1. if statement
+2. if else statement
+3. if elseif else statement
+
+## 1. If statement
+An if statement consists of the conditional statement and the body.  The body will get executed if the conditional statement is true.
+```php
+if ($conditionToCheck) {
+    // Statement body.
+    // This gets executed when the $conditionToCheck is true
+}
+```
+
+The example below will output `It is ready` because the variable `$isReady` is evaluated to true.
+```php
+$isReady = true;
+if ($isReady === true) {
+    // This will run as $isReady is true
+    echo "It is ready";
+}
+```
+The example below will not output `It is ready` because the variable `$isReady` is evaluated to false.
+```php
+$isReady = false;
+if ($isReady === true) {
+    // This will not run as $isReady is false
+    echo "It is ready";
+}
+```
+
+## 2. If else statement
+An if else statement consists of the conditional statement and a else block. The else block is executed if the conditional statement is not met.
+
+```php
+if ($conditionToCheck) {
+    // Statement body.
+    // This gets executed when the $conditionToCheck is true
+} else {
+    // else block.
+    // This gets executed when the $conditionToCheck is false
+}
+```
+
+The example below will set the value of `$settings['api_key]` to `abc_test` because the `$mode` has the value of `test`.
+```php
+$settings = [
+    'api_key' => 'abc_dev'
+];
+
+$mode = 'test';
+if ($mode === 'prod') {
+    $settings = ['api_key'] = 'abc_prod'
+} else {
+    $settings = ['api_key'] = 'abc_test'
+}
+
+```
+## 3. If elseif statement
+An if elseif statement consists of the conditional statement, an elseif block and a else block. The elseif block is executed if the first conditional statement has not been met but its condition has been met.
+
+The else block gets executed when the if condition or the elseif condition has not been met.
+
+```php
+if ($valueToCheck) {
+    // Statement body.
+    // This gets executed when the $valueToCheck is true
+} elseif($anotherValueToCheck) {
+    // elseif block
+    // This gets executed when the $valueToCheck is false but the $anotherValueToCheck condition is true 
+} else {
+    // else block.
+    // This gets executed when the $valueToCheck and the $anotherValueToCheck are both false
+}
+```
+
+The example below will set the value of `$discountAmount` to `20` because the `$discountCode` has the value of `HOWTOCODEWELL`. 
+
+In this example the `elseif` block is executed as the if condition has not met but the `elseif` condition is correct. 
+
+```php
+$discountCode = 'HOWTOCODEWELL';
+
+if ($discountCode === 'BLACKFRIDAY') {
+    $discountAmount = 10;
+} elseif($discountCode === 'HOWTOCODEWELL') {
+    $discountAmount = 20; 
+} else {
+    $discountAmount = 0; 
+}
+```
+
+If there are many possible values for `$discountCode` then a switch statement would be recommended.