a function prototype can always be omitted when:,

A function prototype can always be omitted when the function definition is inside a class declaration, or in a header file. A function prototype is also optional if it only has one parameter which does not have default values, and that argument type matches the corresponding parameter type of the called function. A function prototype is also optional if it only has one parameter which does not have default values, and that argument type matches the corresponding parameter type of the called function. If you are using C++11 or higher, a declaration can always be omitted for any local scope when it has no side effects. This applies to functions with parameters that don’t have default arguments, as well as lambda expressions without return types. This applies to functions with parameters that don’t have default arguments, as well as lambda expressions without return types. When there is an immediate call to a function (e.g., x()), omitting a prototype doesn’t affect anything because the compiler automatically generates code so that this behavior will work correctly – even in cases