Why I am getting error in this code?? And the error is: expected primary-expression before ‘long’

Question

I am getting error in this code while converting the member data of the class Int to long double in the conversion operators. But I don't understand why this happens?

 #include<iostream>
  using namespace std;

 class Int
 {
    private:
         int number;
    public:
        Int() : number(0)                                         // no argument constructor
     {     }

     Int( int i) : number(i)                                 // 1-argument constructor
       {     }

    void putInt()                                           // display Int
     { cout << number; }

     void getInt()                                           // take value from the user
     { cin >> number; }

     operator int()                                           // conversion operator ( Int to int)
     { return number; }

     Int operator + ( Int a)
     { return checkit( long double (number) + long double (a))  ; }  // performs addition of two objects of type Int
    
     Int operator - ( Int a)
     { return checkit(long double (number) - long double (a) ); }  //performs subtraction of two objects of type Int

     Int operator * (Int a)  
     { return checkit( long double (number) * long double (a) ); }  // performs multiplication of two objects of type Int

     Int operator / (Int a)
     { return checkit( long double (number) / long double (a) ); } // performs division of two objects of type Int

     Int checkit( long double answer)
     {
        if( answer > 2147483647.0L || answer < - 2147483647.0L)
          { cout << "\nOverflow Error\n";
             exit(1);
          }

        return Int ( int(answer));
     }
   
 }; 

 int main()
  {
    Int numb1 = 20;
    Int numb2 = 7;
    Int result, cNumber;

    result = numb1 + numb2;
   cout << "\nresult = "; result.putInt();                         //27
  result = numb1 - numb2;
  cout << "\nresult = "; result.putInt();                         //13
   result = numb1 * numb2;
  cout << "\nresult = "; result.putInt();                        // 140
   result = numb1 / numb2;
  cout << "\nresult = "; result.putInt();                        // 2

  cNumber = 2147483647;
   result = numb1 + cNumber;     // overflow error
   cout << "\nresult = "; result.putInt();
   cNumber = -2147483647;
  result = numb1 + cNumber;                                      // overflow error

  cout << endl;
   return 0;

  }

In the operator overloading code for the +, -, * and / operators, I am getting errors of:

expected primary expression before 'long'

I don't understand why this happens.

score 6 · Answer 1 · answered Aug 16 '22 at 09:09

The nature of C++ syntax does not allow type names that consist of more than one word (like long double and unsigned int) to be used in functional casts, as you are attempting to do in the long double (number) and long double (a) expressions. (Just using a plain double type would be OK, though.)

But you really shouldn't be using such casts in a C++ program – they're almost as evil as C-style casts.

Whenever possible, use explicit C++ casts, starting from the 'softest' available option; in your case, static_cast will work for the int to long double conversion as well as any other; so, just change your binary operator functions to forms like the following:

    Int operator + (Int a)
    {
        return checkit(static_cast<long double>(number) + static_cast<long double>(a));
    }  // performs addition of two objects of type Int

Why I am getting error in this code?? And the error is: expected primary-expression before ‘long’

1 Answers1