undefined reference to '__objc_class_name_Fraction'

// Aquire radius value
// Postcondition: print out header and return radius value
double printHeader();

// Precondition: radius has been entered
// Postcondition: calculate and print out area of the circle
void calculateArea(double& radius);

double printHeader(double& radius) { ... }

void calculateArea(double& radius, double area) { ... }

double printHeader(double& radius);
void calculateArea(double& radius, double area);

main: producer.o consumer.o AddRemove.o
   $(COMPILER) -pthread $(CCFLAGS) -o producer.o consumer.o AddRemove.o

main: producer.o consumer.o AddRemove.o
   $(COMPILER) -pthread $(CCFLAGS) -o $@ producer.o consumer.o AddRemove.o

main: producer.o consumer.o AddRemove.o
   $(COMPILER) -pthread $(CCFLAGS) -o $@ $^

//Now you don't need to implement them
virtual void draw() = 0;
virtual void move() = 0;
virtual void scale(double) = 0;

%{
// Your includes...
int yyFlexLexer::yywrap() { return 1; }

// Add definition of yyin
std::istream* yyin;
%}