namespace::function cannot be used as a function - function

Question

main.cpp
#include "Primes.h"
#include <iostream>
int main(){
std::string choose;
int num1, num2;
while(1 == 1){
std::cout << "INSTRUCTIONS" << std::endl << "Enter:" << std::endl
<< "'c' to check whether a number is a prime," << std::endl
<< "'u' to view all the prime numbers between two numbers "
<< "that you want," << std::endl << "'x' to exit,"
<< std::endl << "Enter what you would like to do: ";
std::cin >> choose;
std::cout << std::endl;
if(choose == "c"){
std::cout << "Enter number: ";
std::cin >> num1;
Primes::checkPrimeness(num1) == 1 ?
std::cout << num1 << " is a prime." << std::endl << std::endl :
std::cout << num1 << " isn't a prime." << std::endl << std::endl;
}else if(choose == "u"){
std::cout << "Enter the number you want to start seeing primes "
<< "from: ";
std::cin >> num1;
std::cout << "\nEnter the number you want to stop seeing primes "
<< "till: ";
std::cin >> num2;
std::cout << std::endl;
for(num1; num1 <= num2; num1++){
Primes::checkPrimeness(num1) == 1 ?
std::cout << num1 << " is a prime." << std::endl :
std::cout << num1 << " isn't a prime." << std::endl;
}
}else if(choose == "x"){
return 0;
}
std::cout << std::endl;
}
}
Primes.h
#ifndef PRIMES_H
#define PRIMES_H
namespace Primes{
extern int num, count;
extern bool testPrime;
// Returns true if the number is a prime and false if it isn't.
int checkPrimeness(num);
}
#endif
Primes.cpp
#include "Primes.h"
#include <iostream>
int Primes::checkPrimeness(num){
if(num < 2){
return(0);
}else if(num == 2){
return(1);
}else{
for(count = 0; count < num; count++){
for(count = 2; count < num; count++){
if(num % count == 0){
return(0);
}else{
testPrime = true;
if(count == --num && testPrime == true){
return(1);
}
}
}
}
}
}
I get the following 3 errors: Errors from terminal
I've spent hours for days and still can't seem to fix the errors.
I've tried using extern and pretty much everything I can imagine.

Answer 1

Here is an error in function declaration:
int checkPrimeness(num);
defines a global integer variable checkPrimeness initialized with num! To declare a function you just should change it like:
int checkPrimeness(int);
Can't understand why you declare parameters as external variables. To split declarations and realization you should declare all functions and classes inside header file, and define them inside source file.