revision #1: 更新第二章中已维护的代码

code/2/2.3.if.switch.cpp

@@ -0,0 +1,31 @@
+//
+// 2.3.if.switch.cpp
+// chapter 2 language usability
+// modern cpp tutorial
+//
+// created by changkun at changkun.de
+//
+
+#include <iostream>
+#include <vector>
+#include <algorithm>
+
+int main() {
+    std::vector<int> vec = {1, 2, 3, 4};
+
+    // before c++17, can be simplefied by using `auto`
+    const std::vector<int>::iterator itr = std::find(vec.begin(), vec.end(), 2);
+    if (itr != vec.end()) {
+        *itr = 3;
+    }
+
+    // after c++17, can be simplefied by using `auto`
+    if (const std::vector<int>::iterator itr = std::find(vec.begin(), vec.end(), 3);
+        itr != vec.end()) {
+        *itr = 4;
+    }
+
+    // should output: 1, 4, 3, 4. can be simplefied using `auto`
+    for (std::vector<int>::iterator element = vec.begin(); element != vec.end(); ++element)
+        std::cout << *element << std::endl;
+}