diff --git a/include/s0008_string_to_integer.hpp b/include/s0008_string_to_integer.hpp
new file mode 100644
index 0000000..5ecd22b
--- /dev/null
+++ b/include/s0008_string_to_integer.hpp
@@ -0,0 +1,15 @@
+#ifndef S0008_STRING_TO_INTEGER
+#define S0008_STRING_TO_INTEGER
+
+#include <string>
+#include <unordered_map>
+#include <vector>
+
+using namespace std;
+
+class Solution {
+public:
+    int myAtoi(string s);
+};
+
+#endif
diff --git a/src/s0008_string_to_integer.cpp b/src/s0008_string_to_integer.cpp
new file mode 100644
index 0000000..ef3674f
--- /dev/null
+++ b/src/s0008_string_to_integer.cpp
@@ -0,0 +1,39 @@
+#include "s0008_string_to_integer.hpp"
+
+// 当流程很复杂的时候，画流程图: https://paste.sainnhe.dev/NQxx.png
+
+class Automaton {
+  string state = "start";
+  unordered_map<string, vector<string>> table = {
+      {"start", {"start", "signed", "in_number", "end"}},
+      {"signed", {"end", "end", "in_number", "end"}},
+      {"in_number", {"end", "end", "in_number", "end"}},
+      {"end", {"end", "end", "end", "end"}}};
+
+  int get_col(char c) {
+    if (isspace(c)) return 0;
+    if (c == '+' or c == '-') return 1;
+    if (isdigit(c)) return 2;
+    return 3;
+  }
+
+ public:
+  int sign = 1;
+  long long ans = 0;
+
+  void get(char c) {
+    state = table[state][get_col(c)];
+    if (state == "in_number") {
+      ans = ans * 10 + c - '0';
+      ans = sign == 1 ? min(ans, (long long)INT_MAX)
+                      : min(ans, -(long long)INT_MIN);
+    } else if (state == "signed")
+      sign = c == '+' ? 1 : -1;
+  }
+};
+
+int Solution::myAtoi(string str) {
+  Automaton automaton;
+  for (char c : str) automaton.get(c);
+  return automaton.sign * automaton.ans;
+}
diff --git a/tests/s0008_string_to_integer.cpp b/tests/s0008_string_to_integer.cpp
new file mode 100644
index 0000000..6ab0bb3
--- /dev/null
+++ b/tests/s0008_string_to_integer.cpp
@@ -0,0 +1,24 @@
+#include "s0008_string_to_integer.hpp"
+
+#include <gtest/gtest.h>
+
+TEST(Problem8, Case1) {
+  string i = std::string("42");
+  int o = 42;
+  Solution solution;
+  EXPECT_EQ(solution.myAtoi(i), o);
+}
+
+TEST(Problem8, Case2) {
+  string i = std::string("   -42");
+  int o = -42;
+  Solution solution;
+  EXPECT_EQ(solution.myAtoi(i), o);
+}
+
+TEST(Problem8, Case3) {
+  string i = std::string("4193 with words");
+  int o = 4193;
+  Solution solution;
+  EXPECT_EQ(solution.myAtoi(i), o);
+}