add multiple conditions - thanks slass and vital

content/multiple-conditions.md

@@ -1 +1,52 @@
-TBD
+To optimize your code and check for multiple conditions at once, you can use `if and`.
+
+The `if and` statement allows up to `8` conditional instructions and executes the code only if _all_ of them return true:
+
+```sb
+if and
+    is_key_pressed 114
+    is_key_pressed 115
+then
+    // This code will execute only if both `F3` and `F4` keys are pressed.
+end
+```
+
+Similarly, the `if or` statement also allows up to `8` conditional instructions but executes the code if any one of them returns true:
+
+```sb
+if or
+    is_key_pressed 114
+    is_key_pressed 115
+then
+    // This code will execute if either `F3` or `F4` key is pressed.
+end
+```
+
+Unlike many programming languages, conditions in GTA scripts are not [lazy](https://en.wikipedia.org/wiki/Lazy_evaluation). The game will always evaluate all of them. It may result in a crash if conditions assume the result of the preceding conditions. For example, you can't check if a character exists and then check its location in the same if statement:
+
+```sb
+if and
+    does_char_exist testChar
+    not locate_char_any_means_char_3d testChar plc 100.0 100.0 100.0 false
+then
+...
+end
+```
+
+This will crash the game if the character doesn't exist because the game will still try to check its location using an invalid handle.
+
+<img src="/img/lazy-crash.png" alt="SCRLog Crash report" />
+
+Instead, you should split these checks into separate if statements:
+
+```sb
+if 
+    does_char_exist testChar
+then
+    if 
+        not locate_char_any_means_char_3d testChar plc 100.0 100.0 100.0 false
+    then
+        ...
+    end
+end
+```