implement a sum with controlled inputs

exercises/sum.cpp

@@ -6,3 +6,57 @@
   Insert the second number: 2
   Sum: 3
 */
+
+#include <iostream>
+
+using namespace std;
+
+const int ZERO = 48;
+const int NINE = 57;
+const int MAX_DIGIT = 10;
+const int MINUS = 45;
+
+const string ERROR_COLOR = "\033[31m";
+const string NORMAL_COLOR = "\033[0m";
+
+template <typename T>
+T sumNumber(T n1, T n2);
+double insertNumber(const string& msg);
+bool checkStringIsNumber(string in);
+
+
+int main() {
+  auto n1 = insertNumber("Insert first number:");
+  auto n2 = insertNumber("Insert second number:");
+  auto ris = sumNumber(n1, n2);
+  cout << "Sum: " << ris;
+}
+
+template <typename T>
+T sumNumber(T n1, T n2) {
+  return n1 + n2;
+}
+
+double insertNumber(const string& msg){
+  string insert;
+  bool isCorrect = true;
+  do {
+    if(!isCorrect) cout << ERROR_COLOR << "[Insert a valid input] " << NORMAL_COLOR;
+    cout << msg;
+    getline(cin, insert);
+  } while(!(isCorrect = checkStringIsNumber(insert)));
+
+  return stod(insert);
+}
+
+bool checkStringIsNumber(string in){
+  if(in.empty()) return false;
+  if(in.size() > MAX_DIGIT) return false;
+  for (size_t i = 0; i < in.size(); ++i){
+    if ((in[i] < ZERO || in[i] > NINE)){
+      if (i == 0 && in[i] == MINUS) continue;
+      return false;
+    }
+  }
+  return true;
+}