Calculator with single line input - follow-up

Question

Part 2 of this question. I've rewritten most parts of the code, for the better I hope. The code now has some more logic and less readability.

Functions included in the calculator:

• Addition
  User input 2+2 Program output 4

• Subtraction
  User input 2-2 Program output 0

• Multiplication
  User input 2*2 Program output 4

• Division
  User input 2/2 Program output 1

• Exponentiation
  User input 2^2 Program output 4

#include <iostream>
#include <string>
#include <sstream>
#include <Windows.h>
#include <cmath>
class Math_Functions
{
public:
 double addition(double, double);
 double subtraction(double, double);
 double multiplication(double, double);
 void division(double, double);
 void exponentiation(double, double);
} math;
class Results_Handler
{
public:
 void division(std::string);
 void exponentiation(std::string);
} res_handler;
//This function I found somewhere in the deep internet
class Miscellaneous
{
public:
 void Pause()
 {
 std::cout << std::endl << "Press any key to continue . . . ";
 std::cin.sync();
 std::cin.ignore();
 }
 void ClearScreen()
 {
 HANDLE hStdOut;
 CONSOLE_SCREEN_BUFFER_INFO csbi;
 DWORD count;
 DWORD cellCount;
 COORD homeCoords = { 0, 0 };
 hStdOut = GetStdHandle(STD_OUTPUT_HANDLE);
 if (hStdOut == INVALID_HANDLE_VALUE) return;
 /* Get the number of cells in the current buffer */
 if (!GetConsoleScreenBufferInfo(hStdOut, &csbi)) return;
 cellCount = csbi.dwSize.X *csbi.dwSize.Y;
 /* Fill the entire buffer with spaces */
 if (!FillConsoleOutputCharacter(
 hStdOut,
 (TCHAR) ' ',
 cellCount,
 homeCoords,
 &count
 )) return;
 /* Fill the entire buffer with the current colors and attributes */
 if (!FillConsoleOutputAttribute(
 hStdOut,
 csbi.wAttributes,
 cellCount,
 homeCoords,
 &count
 )) return;
 /* Move the cursor home */
 SetConsoleCursorPosition(hStdOut, homeCoords);
 }
} misc;
//Handle the result from division and cout correspondingly
void Results_Handler::division(std::string inPut)
{
 if (inPut != "Error")
 {
 std::cout << inPut;
 }
 else
 {
 std::cout << "Come on, you know you can't divide by 0...";
 }
}
//Handle the result from the exponentiation and cout correspondingly
void Results_Handler::exponentiation(std::string inPut)
{
 if (inPut != "Error")
 {
 std::cout << inPut;
 }
 else
 {
 std::cout << "You can't exponentiate by negative numbers.";
 }
}
double Math_Functions::addition(double a, double b)
{
 return a + b;
}
double Math_Functions::subtraction(double a, double b)
{
 return a - b;
}
double Math_Functions::multiplication(double a, double b)
{
 return a * b;
}
void Math_Functions::division(double a, double b)
{
 //Dividing by 0 = universe explodes
 if (b == 0)
 {
 res_handler.division("Error");
 }
 else
 {
 double c = a / b;
 std::stringstream result;
 result << c;
 res_handler.division(result.str());
 }
}
void Math_Functions::exponentiation(double a, double b)
{
 //If the number you're exponentiating with is 0 the result is always 1
 if (b == 0)
 {
 res_handler.exponentiation("1");
 }
 //If you're exponentiating with 1 the result is the same number
 else if (b == 1)
 {
 std::stringstream res;
 res << a;
 res_handler.exponentiation(res.str());
 }
 else
 {
 std::stringstream res;
 res << pow(a, b);
 res_handler.exponentiation(res.str());
 }
}
int main()
{
 //Declare variables
 double a, b;
 char function;
 std::string line;
 while (true)
 {
 misc.ClearScreen();
 std::getline(std::cin, line);
 //Check if the input is empty and ignore
 if (line.empty())
 {
 continue;
 }
 //Check if the input is either 'q' or 'Q' and break loop
 else if (line[0] == 'q' || line[0] == 'Q')
 {
 break;
 }
 //Else if everything is OK extract data
 else
 {
 std::istringstream inStream(line);
 inStream >> a;
 inStream >> function;
 inStream >> b;
 //Check for bad input and print error
 if (!inStream || function != '+' && function != '-' && function != '*' && function != '/' && function != '^')
 {
 std::cerr << "\"" << line << "\" is invalid input";
 }
 }
 //Check what the user wants to do
 switch (function)
 {
 case '+': std::cout << math.addition(a, b); break;
 case '-': std::cout << math.subtraction(a, b); break;
 case '*': std::cout << math.multiplication(a, b); break;
 case '/': math.division(a, b); break;
 case '^': math.exponentiation(a, b); break;
 }
 misc.Pause();
 }
 return 0;
}

• Jamal: The request for a library is not on-topic here, nor is it anywhere on SE. You may just have to search for something yourself and try to implement it here.

Answer 1

The singleton pattern:

Your classes Math_Functions, Results_Handler and Miscellaneous seem like an attempt at the singleton pattern (see 1 and 2). Your approach of declaring a global instance of each class is also valid, but has a few drawback and is not very conventional.

Since your classes hold no member data and the class is really just serving as a name space for the functions, I would use an actual namespace instead and don't even bother with a full-blown singleton implementation in this case. Example:

namespace math
{
 double addition(double, double);
 double subtraction(double, double);
 double multiplication(double, double);
 void division(double, double);
 void exponentiation(double, double);
} // namespace

Then to access each function you now have to use the :: (namespace resolution) operator: math::addition(a, b);

Miscellaneous tips:

• Keep parameter names in function prototypes. This adds to the code documentation.

• Be consistent with your naming convention. You have both PascalCase and camelCase names for functions/methods. Choose one and use it consistently.

• Functions from <cmath>, such as pow(), should be accessed using the fully qualified name with the std:: prefix. I.e.: std::pow().

• Consider splitting your project in a few separate source files. There is quite a bit of code here already to be kept all in the same source file. You should ideally place each class in its own .cpp/.h pair.

• Returning zero at the end of main is optional. If you don't do it explicitly, the compiler will default to a return 0.

• skorpi7478: I really want to separate the code in different files, but the problem is I don't know how (yet). I can include other .cpp files in the main, but this way it doesn't make much sense to me. Thanks for the guidelines :)
• glampert: @skorpi7478, Well, take a look at how to do that in your IDE/compiler. You will then have the class implementation in a .CPP file and the declaration in a header file (.H); Then you include the .H in your other sources files, such as in main.cpp.