diff --git a/code_style_guideline/code_style_guideline.md b/code_style_guideline/code_style_guideline.md
index 29b5fe6..d61a73a 100644
--- a/code_style_guideline/code_style_guideline.md
+++ b/code_style_guideline/code_style_guideline.md
@@ -553,6 +553,51 @@ struct Stack<T> { ... }
 func write<target: OutputStream>(to target: inout target)
 func swap<Thing>(_ a: inout Thing, _ b: inout Thing)
 ```
+### Loops
+### 1. Where Clause
+Prefer to use where clause if it's possible.
+
+**Preferred**:
+```swift
+for item in items where item.productCount > 1 {
+    ...
+}
+```
+
+**Not Preferred**:
+```swift
+for item in items {
+    if item.productCount > 1 {
+        
+    }
+}
+```
+
+### 2. Indices
+Use .indicies property to loop over array indexes.
+
+**Preferred**:
+```swift
+for index in array.indices {
+    
+}
+```
+
+**Not Preferred**:
+```swift
+for index in 0..<array.count {
+    
+}
+```
+
+### 3. Enumarated
+Use .enumarated to loop through both index and item.
+
+```swift
+for (index, item) in array.enumarated() {
+    
+}
+```
 
 ### Class and Structs
 ### 1. Controller Suffix