Update main.cpp

src/main.cpp

@@ -10,21 +10,36 @@
  * Adds two integers
  */
 int add(const int a, const int b) {
-  return a + b;
+  int res;
+  bool overflow = __builtin_sadd_overflow(a, b, &res);
+  if (overflow) {
+    throw std::invalid_argument("Malformed input. Integer overflow (add).");
+  }
+  return res;
 }
 
 /*
- * Subtracts integer b from integer a
+ * Multiplies two integers
  */
-int subtract(const int a, const int b) {
-  return b - a;
+int multiply(const int a, const int b) {
+  int res;
+  bool overflow = __builtin_smul_overflow(a, b, &res);
+  if (overflow) {
+    throw std::invalid_argument("Malformed input. Multiplication error.");
+  }
+  return res;
 }
 
 /*
- * Multiplies two integers
+ * Subtracts integer b from integer a
  */
-int multiply(const int a, const int b) {
-  return a * b;
+int subtract(const int a, const int b) {
+  int res;
+  bool overflow = __builtin_ssub_overflow(b, a, &res);
+  if (overflow) {
+    throw std::invalid_argument("Malformed input. Integer overflow (subtract).");
+  }
+  return res;
 }
 
 /*
@@ -33,7 +48,7 @@ int multiply(const int a, const int b) {
  */
 int divide(const int a, const int b) {
   if (b == 0) {
-    throw std::invalid_argument("Tried to divide by 0.");
+    throw std::invalid_argument("Malformed input. Division by zero.");
   }
   return a / b;
 }
@@ -41,7 +56,6 @@ int divide(const int a, const int b) {
 using binary_operator = decltype(&add);
 
 int evaluate(const std::string &s) {
-  std::stack<int> stack;
   static const std::unordered_map<char, binary_operator> map {
     {'+', add},
     {'-', subtract},
@@ -49,6 +63,8 @@ int evaluate(const std::string &s) {
     {'/', divide}
   };
   decltype(map)::iterator iter;
+  std::stack<int> stack;
+
   for (char c : s) {
     if (std::isdigit(c)) {
       stack.push(c - '0');
@@ -91,7 +107,6 @@ int main() {
   } catch (const std::exception &e) {
     std::cout << e.what();
   }
-
   if (result != INT_MAX) {
     std::cout << "Result is: " << result << '\n';
   }