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This worksheet is for your use during and after lecture. It will not be collected or graded, but I think you will find it a useful tool as you learn C++ and study for the exams. Explain all false answers for the “True or False” questions; in general, show enough work and provide enough explanation so that this sheet is a useful pre-exam review. I will be happy to review your answers with you during office-hours, via Email, or instant messaging.
- Name six binary operators in C++.
Solution: Addition, subtraction, multiplication, division, modulus, input (<<), or output (>>).
- When binary operators are overloaded by global functions: (a) True or False: Both operands must be of the same class.
Solution: False.
(b) True or False: The calling object is on the left of the operation symbol.
Solution: False. There is no calling object for global operators.
(c) True or False: The operator should return one of the arguments provided.
Solution: False. Only the case for << or >>.
(d) True or False: The operator must be written in some class’ scope.
Solution: False. The function is global, it cannot be in any class’ scope.
- (a) Write the protoype of a friend global operator for taking the modulus of a myClass object (LHS) and an integer (RHS). It should return an integer value.
Solution: friend int operator%( const myClass&, int rhs );
(b) Where would you find the answer to part a within myClass’ source files?
Solution: In myClass.h, within the class declaration (required since it is a friend function).
(c) Write the protoype of a global operator for multiplying an integer (LHS) with a myClass object (RHS). It should return a new myClass object.
Solution: myClass operator*( int lhs, const myClass& rhs );
(d) Where would you find the answer to part c within myClass’ source files?
Solution: In myClass.h but outside of the class declaration (required since it is not a friend function).
(e) Assume myClass has a default constructor. Write a snippet of C++ that would invoke the two global operators prototyped in parts a and c.
Solution: myClass a ; int b ; int i = a % b ; myClass c = i * a ;
- The friend keyword may occur in C++ source only between the curly braces of what?
Solution: A class declaration.
- The following is the function header of a global operator:
int operator-( const myClass& lhs, int rhs ) Is the operator a friend of myClass or not? A. Certainly not. B. Maybe, I could tell for sure if I saw the function implementation. C. Maybe, I could tell for sure if I saw the myClass declaration.
Solution: C — the only way to be absolutely sure is to see the myClass declaration.
Solution:
include < iostream >
using namespace std ; / ∗ ∗∗ ∗ A c o m p l e x number c l a s s w i t h o p e r a t o r o v e r l o a d i n g. We make l i f e s i m p l e , and ∗ p u t e v e r y t h i n g i n t o p u b l i c so we don ’ t hav e t o w r i t e 4 s e p a r a t e a c c e s s o r ∗ f u n c t i o n s. ∗ ∗ PLEASE t h i n k a b o u t t h i s : ∗ 1. T h e r e a r e no v a l u e s f o r r e a l and i m ag t h a t c r e a t e an I N V A LI D c o m p l e x ∗ number. ∗ 2. The c o m p l e x c l a s s does n ’ t hav e any d a t a members w i t h DEPENDENCE on any ∗ o t h e r d a t a members. T h e r e i s no ∗ CONSISTENCY ∗ we m us t m a i n t a i n! So we ∗ don ’ t need t o make. r e a l and. i m ag p r i v a t e! ∗ ∗ I hav e a r b i t r a r i l y c hoos en t o make o p e r a t o r + and o p e r a t o r ∗ f r i e n d f u n c t i o n s. ∗ ∗ / class complex { public : double real , imag ; complex (); complex ( double r , double i ); friend complex operator +( const complex & lhs , const complex & rhs ); friend complex operator *( const complex & lhs , const double & rhs ); };
/ / G l o b a l o u t p u t f u n c t i o n −−− my math r e f e r e n c e us es ( , ) n o t a t i o n. / / S i n c e e v e r y t h i n g i s p u b l i c , we don ’ t need t o f r i e n d t h i s. ostream & operator < <( ostream & os , const complex & rhs ) { return os << " ( " << rhs. real << " ," << rhs. imag << " ) " ; } / / F o r c o m p l e t e n e s s , s u p p o r t a l p h a ∗ z complex operator *( const double lhs , const complex & rhs ) { / / r e t u r n an anonymous o b j e c t return complex ( lhs * rhs. real , lhs * rhs. imag ); }
/ / c t o r s complex :: complex ( double r , double i ) : real ( r ) , imag (i ) { / ∗ em pt y ∗ / } complex :: complex ( ) : real (0) , imag (0) { / ∗ em pt y ∗ / }
/ / ops complex operator +( const complex & lhs , const complex & rhs ) { / / r e t u r n an anonymous o b j e c t return complex ( lhs. real + rhs. real , lhs. imag + rhs. imag ); }
complex operator *( const complex & lhs , const double & rhs ) { / / r e t u r n an anonymous o b j e c t return complex ( lhs. real * rhs , lhs. imag * rhs ); }
