C++ Error: "member Engine::x is not a type name" -

i'm bulding standard 4 func calculator, , i'm trying pass 2 numbers off parameters user has entered. within engine.h class have declared

float num1, num2; 

and have function

float add(num1, num2); 

in these params, num1 , num2 both have error stated in title: "error: member engine::num1 not type name." i'm confused why these bringing errors, isn't how parameters work?

simply declare member function as

float add() const; 

as function deal data members num1 , num2 needs no parameters. example defined as

float engine::add() const {     return num1 + num2; } 

as error forgot write type specifiers of parameters.

instead of

float add(num1, num2); 

there shall @ least

float add( float num1, float num2);