diff --git a/lib/add.js b/lib/add.js
index 1714b95..e24532a 100644
--- a/lib/add.js
+++ b/lib/add.js
@@ -1,5 +1,16 @@
-function add() {
+function add(num1, num2) {
   // 实现该函数
+  let res = ''
+  let i = num1.length - 1, j = num2.length - 1, flag = 0
+  while (i >= 0 || j >= 0 || flag !== 0) {
+      if (i >= 0) flag += num1.charCodeAt(i--) - 48
+      if (j >= 0) flag += num2.charCodeAt(j--) - 48
+      res = '' + flag % 10 + res
+      flag /= 10
+      // 向下取整
+      flag = ~~flag
+  }
+  return res
 }
 
 module.exports = add
\ No newline at end of file