Exception handling classes in C++ - c++

Question

I have an assignment for my OOP class to create a rudimentary calculator. The goal of the assignment is to practice namespaces and exception handling.
I will paste the text of the problem for clarity:
You have to implement the class Kalkulator which solves rudimentary mathematical expressions and returns the result as an integer.
The class Kalkulator should be put in a namespace called Matematika. The whole class needs to be implemented in the header file without a .cpp file.
You have to define two exceptions and throw them in the correct situation(they are caught in the main function)
IncorrectDataExc put the class into the namespace Matematika->Exceptions
InvalidOperationExc put the class into the namespace Matematika->Exceptions
and they also gave me the main function:
#include <iostream>
#include <string>
#include "Kalkulator.h"
#include "IncorrectDataExc.h"
#include "InvalidOperationExc.h"
using namespace std;
int main()
{
string s;
getline(cin, s);
try
{
Matematika::Kalkulator kalkulator;
cout << kalkulator.izracunaj(s) << endl;
}
catch(Matematika::Exceptions::IncorrectDataExc)
{
cout << "Exception IncorrectData" << endl;
}
catch(Matematika::Exceptions::InvalidOperationExc)
{
cout << "Exception InvalidOperation" << endl;
}
return 0;
}
The problem I'm having is that i don't know what to throw when i get an exception and i don't know how the InvalidOperationExc and IncorrectDataExc classes should look like because i don't know what the catch functions are actually catching(an object?)
I have to create 3 header files:
IncorrectDataExc.h
InvalidOperationExc.h
Kalkulator.h
This is what i have so far
#pragma once
#include <string>
#include <sstream>
using namespace std;
namespace Matematika{
class Kalkulator{
private:
public:
int izracunaj(string mojString)
{
int prviBroj = 0;
int drugiBroj = 0;
char operacija = ' ';
stringstream ss(mojString);
ss >> prviBroj >> operacija >> drugiBroj;
if(operacija != '*' && operacija != '+' && operacija != '/' && operacija != '-')
{
Matematika::Exceptions::InvalidOperationExc greska1;
throw greska1;
}
if(prviBroj % drugiBroj != 0)
{
Matematika::Exceptions::IncorrectDataExc greska2;
throw greska2;
}
}
};
}
and I'm getting some errors:
'Exceptions': the symbol to the left of a '::' must be a type
'InvalidOperationExc' : is not a member of 'Matematika'
'InvalidOperationExc' : undeclared identifier
missing ';' before identifier 'greska1'
'greska1' : undeclared identifier
'greska1' : undeclared identifier
I don't know what I'm doing wrong. The part that is confusing me the most is this
catch(Matematika::Exceptions::IncorrectDataExc)
what is the catch function receiving?

Answer 1

Pretty self explanatory errors:
'InvalidOperationExc' : is not a member of 'Matematika'
In other words, it doesn't exist. This
Matematika::Exceptions::InvalidOperationExc greska1;
resulted in the error. You should either change the InvalidOperationExc to something else or create it in Matematika.

Answer 2

int izrakunaj() doesn't need Matematika::... to access members of namespace Matematika because it is also a member.
namespace ns
{
int integer; //ns::integer
void set0(){integer=0;} //modifies the variable above
void set1(){ns::integer=1;} //modifies the variable below
namespace ns
{
int integer; //ns::ns::integer
}
}