From 270aead8e2cca7e8895afb7a87daffdfaaa0e205 Mon Sep 17 00:00:00 2001
From: Haoshen Zhong <124694738@qq.com>
Date: Sat, 10 Aug 2019 12:06:24 +0800
Subject: [PATCH] Update common-tricks.md

---
 docs/intro/common-tricks.md | 29 +++++++++++++++++++++++++++++
 1 file changed, 29 insertions(+)

diff --git a/docs/intro/common-tricks.md b/docs/intro/common-tricks.md
index 0c64264c..0afcaea7 100644
--- a/docs/intro/common-tricks.md
+++ b/docs/intro/common-tricks.md
@@ -34,6 +34,35 @@
     // 不如
     for (int i = 0; i < n; ++i) res = res OP(a[i] OP a[i + 1]);
     ```
+    
+## 循环宏定义
+
+我们写代码时，像下面这样的循环代码写得会非常多：
+
+```cpp
+for(int i = 0; i < N; i++) {}
+```
+
+为了简化这样的循环代码，我们可以使用宏定义：
+
+```cpp
+#define _for(i, a, b) for(int i = (a); i < (b); ++i)
+```
+
+这样写循环代码时，就可以简化成 `_for(i, 0, N)`。例如：
+
+```cpp
+vector b;
+_for(i, 1, a.size()) {...}
+```
+
+另外推荐一个比较有用的宏定义：
+
+```cpp
+#define _rep(i, a, b) for(int i=(a); i <= (b); ++i)
+```
+
+> 注：参考《算法竞赛入门经典 习题与解答》
 
 ## 善用 namespace
 
-- 
2.11.0