implement a sum with controlled inputs

exercises/sum.cpp

@@ -6,3 +6,77 @@
   Insert the second number: 2
   Sum: 3
 */
+
+#include <iostream>
+#include <string>
+
+using namespace std;
+
+// --- Costant ---
+const int ASCII_ZERO = 48;
+const int ASCII_NINE = 57;
+const int MAX_DIGITS = 10;
+const int ASCII_MINUS = 45;
+
+const string COLOR_ERROR = "\033[31m";
+const string COLOR_RESET = "\033[0m";
+
+// --- Prototype ---
+template <typename T>
+T sumNumber(T n1, T n2);
+
+double promptNumber(const string& msg);
+bool isValidNumber(const string& in);
+
+// --- Main ---
+int main() {
+  double n1 = promptNumber("Insert first number:");
+  double n2 = promptNumber("Insert second number:");
+
+  double ris = sumNumber(n1, n2);
+  cout << "Sum: " << ris << endl;
+
+  return EXIT_SUCCESS;
+}
+
+// --- Template Function ---
+template <typename T>
+T sumNumber(T n1, T n2) {
+  return n1 + n2;
+}
+
+// --- User Validate Input ---
+double promptNumber(const string& msg){
+  string insert;
+  bool valid = true;
+
+  do {
+    if(!valid)
+      cout << COLOR_ERROR << "[Insert a valid input] " << COLOR_RESET;
+
+    cout << msg;
+    getline(cin, insert);
+
+    valid = isValidNumber(insert);
+  } while(!valid);
+
+  return stod(insert);
+}
+
+// --- Validate Numeric String
+bool isValidNumber(const string& in){
+  if(in.empty())
+    return false;
+  if(in.size() > MAX_DIGITS)
+    return false;
+
+  for (int i = 0; i < in.size(); ++i){
+    if ((in[i] < ASCII_ZERO || in[i] > ASCII_NINE)){
+      if (i == 0 && in[i] == ASCII_MINUS)
+        continue;
+      return false;
+    }
+  }
+
+  return true;
+}