Tweaked the error message a bit

Makefile

@@ -2,11 +2,11 @@ all:
 	cc command.cpp input_resolver.cpp main.cpp -lstdc++ -std=c++17 -O3 -L./ -lCalc -o calculator 
 
 libs:
-	cc -c -fPIC basecalc.cpp Operation.cpp
+	cc -c -fPIC basecalc.cpp Operation.cpp special_calculator.cpp
-	cc -shared basecalc.o Operation.o -o libCalc.so
+	cc -shared basecalc.o Operation.o special_calculator.o -o libCalc.so
 
 compile:
 	cc *.cpp -O3 -c
 
 debug:
-	cc *.cpp -g -std=c++17 -o calculator -lstdc++
+	cc *.cpp -g -std=c++17 -o calculator -lstdc++ -lm

Operation.h

@@ -1,3 +1,5 @@
+#pragma once
+
 enum class OpType
 {
     Addition, Subtraction, Multiplication, Division, Modulo, Special

basecalc.cpp

@@ -1,4 +1,5 @@
 #include "basecalc.h"
+#include <iostream>
 
 BaseCalculator::~BaseCalculator()
 {}
@@ -20,11 +21,23 @@ int BaseCalculator::calculate(const Operation& op)
         break;
 
         case OpType::Division:
+        if (op.b == 0)
+        {
+            std::cerr << "Invalid operation requested! Resetting the accumulator to 0\n";
+            result = 0;
+        }
+        else
             result = op.a / op.b;
         break;
 
         case OpType::Modulo:
-        result += op.a % op.b;
+        if (op.b == 0)
+        {
+            std::cerr << "Invalid operation requested! Resetting the accumulator to 0\n";
+            result = 0;
+        }
+        else
+            result = op.a % op.b;
         break;
 
         case OpType::Special:

basecalc.h

@@ -1,3 +1,5 @@
+#pragma once
+
 #include "Operation.h"
 class BaseCalculator
 {

command.h

@@ -1,3 +1,5 @@
+#pragma once
+
 class Command
 {
     public:

input_resolver.cpp

@@ -1,6 +1,7 @@
 #include "input_resolver.h"
 #include <string>
 #include <iostream>
+#include <sstream>
 
 #define delimiter " "
 
@@ -47,10 +48,10 @@ ValidationResult validate_token(const std::string &token)
 
     
     if (digitpos == -1)
-        return {true, ' ', 0};
+        return {true, token[0], 0};
 
     int next = stoi(token.substr(digitpos));
-    return {true, ' ', next};
+    return {true, token[0], next};
 }
 
 Command resolveCommand()
@@ -63,21 +64,28 @@ Command resolveCommand()
     auto validation_result = validate_token(token);
     if (!validation_result.ok())
     {
-        throw std::runtime_error{"invalid token " + validation_result.incorrect_token()};
+        std::ostringstream os;
+        os << "invalid token "<< validation_result.incorrect_token();
+        throw std::runtime_error{os.str()};
     }
 
     bool shouldQuit = token.find("q") != token.npos;
     bool shouldPrint = token.find("p") != token.npos;
-    char operation;
+    char operation = 0;
 
     for (const char c: token)
     {
-        static const std::string operators {"+-*/%"};
+        static const std::string operators {"+-*/%$"};
         if(operators.find(c) != operators.npos)
         {
             operation = c;
         }
     }
 
+    if (operation == 0)
+    {
+        operation = '+';
+    }
+
     return {shouldQuit, operation, validation_result.next_arg(), shouldPrint};
 }

input_resolver.h

@@ -1,2 +1,4 @@
+#pragma once
+
 #include "command.h"
 Command resolveCommand();

main.cpp

@@ -1,17 +1,18 @@
 #include <iostream>
 #include "basecalc.h"
+#include "special_calculator.h"
 #include <memory>
 #include "input_resolver.h"
 
 int main()
 {
-    auto calc = std::make_unique<BaseCalculator>();
+    std::unique_ptr<BaseCalculator> calc = std::make_unique<SpecialCalculator>();
 
-    std::cout << "Initializing calculator";
+    std::cout << "Initializing calculator\n";
 
     while (true)
     {
-        std::cout << "What's your next input? (+,-,*,/,%,$,q,p)";
+        std::cout << "What's your next input? (+,-,*,/,%,$,q,p): ";
         auto command = resolveCommand();
 
         if (command.shouldTerminate())

special_calculator.cpp

@@ -0,0 +1,7 @@
+#include "special_calculator.h"
+#include <cmath>
+
+int SpecialCalculator::special(int a)
+{
+    return sqrt(a);
+} 

special_calculator.h

@@ -1,3 +1,5 @@
+#pragma once
+
 #include "basecalc.h"
 
 class SpecialCalculator: public BaseCalculator