Retranslate the complete English edition from Simplified Chinese (#2010)

* Retranslate the complete English edition from Simplified Chinese

* Polish three English explanations after reader-focused review

en/codes/cpp/chapter_computational_complexity/recursion.cpp

@@ -8,12 +8,12 @@
 
 /* Recursion */
 int recur(int n) {
-    // Termination condition
+    // Base case
     if (n == 1)
         return 1;
-    // Recurse: recursive call
+    // Recurse: make a recursive call
     int res = recur(n - 1);
-    // Return: return result
+    // Unwind: return the result
     return n + res;
 }
 
@@ -22,14 +22,14 @@ int forLoopRecur(int n) {
     // Use an explicit stack to simulate the system call stack
     stack<int> stack;
     int res = 0;
-    // Recurse: recursive call
+    // Recurse: make a recursive call
     for (int i = n; i > 0; i--) {
-        // Simulate "recurse" with "push"
+        // Simulate recursive calls by pushing onto the stack
         stack.push(i);
     }
-    // Return: return result
+    // Unwind: return the result
     while (!stack.empty()) {
-        // Simulate "return" with "pop"
+        // Simulate unwinding by popping from the stack
         res += stack.top();
         stack.pop();
     }
@@ -39,40 +39,40 @@ int forLoopRecur(int n) {
 
 /* Tail recursion */
 int tailRecur(int n, int res) {
-    // Termination condition
+    // Base case
     if (n == 0)
         return res;
-    // Tail recursive call
+    // Tail-recursive call
     return tailRecur(n - 1, res + n);
 }
 
 /* Fibonacci sequence: recursion */
 int fib(int n) {
-    // Termination condition f(1) = 0, f(2) = 1
+    // Base cases: f(1) = 0, f(2) = 1
     if (n == 1 || n == 2)
         return n - 1;
-    // Recursive call f(n) = f(n-1) + f(n-2)
+    // Recursive calls: f(n) = f(n-1) + f(n-2)
     int res = fib(n - 1) + fib(n - 2);
-    // Return result f(n)
+    // Return the result f(n)
     return res;
 }
 
-/* Driver Code */
+/* Driver code */
 int main() {
     int n = 5;
     int res;
 
     res = recur(n);
-    cout << "\nRecursive function sum result res = " << res << endl;
+    cout << "\nSum from the recursive function, res = " << res << endl;
 
     res = forLoopRecur(n);
-    cout << "\nUsing iteration to simulate recursive sum result res = " << res << endl;
+    cout << "\nSum from simulating recursion with iteration, res = " << res << endl;
 
     res = tailRecur(n, 0);
-    cout << "\nTail recursive function sum result res = " << res << endl;
+    cout << "\nSum from the tail-recursive function, res = " << res << endl;
 
     res = fib(n);
-    cout << "\nThe " << n << "th term of the Fibonacci sequence is " << res << endl;
+    cout << "\nFibonacci term " << n << " is " << res << endl;
 
     return 0;
 }