Vfrdtyky

just started off with c++, and stackoverflow for that matter.
any and help infinitely appreciated, apologies in advance if i ask something super dumb

I'm making a program to solve a problem. How many 8 digit numbers are divisible by 18 and are only comprised of the digits 1, 2 and 3. I can generate numbers, but when calling a function i made to use modulus to determine whether they're divisible by 18 or not, the function gives me the error in the title. my code is as follows:

main.cpp

#include <iostream>

#include "functions.h"

using namespace std;



int main()

{

    functions f();

    for(int a = 1; a<4; a++){

    for(int b = 1; b<4; b++){

    for(int c = 1; c<4; c++){

    for(int d = 1; d<4; d++){

    for(int e = 1; e<4; e++){

    for(int f = 1; f<4; f++){

    for(int g = 1; g<4; g++){

    for(int h = 1; h<4; h++){

        int number = 10000000*a + 1000000*b + 100000*c + 10000*d + 1000*e + 100*f + 10*g + h; //generates 8 digit numbers, only using the digits 1 2 and 3

        cout << number << endl; //prints numbers

        int y = 10; //to test this bloody function

        cout << f.modu18()(y); //returns 0 or 1 from func

}}}}}}}}}

functions.h

#ifndef FUNCTIONS_H

#define FUNCTIONS_H

#include <iostream>



using namespace std;



class functions

{

    public:

        functions();

        string modu18(int x);

    protected:

    private:

};



#endif

functions.cpp

#include "functions.h"

#include <iostream>



using namespace std;



functions::functions(){



    cout << "Functions initialised!" << endl; //to see if this thing is actually loading



}



string functions::modu18(int x){ //this is checking whether the number is divisible by 18

    if(x % 18 == 0){

        return 0;

    }else{

        return 1;

    };

} //btw, using multiple files becuase i want to learn how to make this work for the future

The exact error returned when compiling is

request for member 'modu18' in 'f', which is of non-class type 'int'

I have no clue why this is saying this, all my data types are correct, for the data and the function types.
send help pls
Many thanks.

In your function main there are two different f:

First one here

functions f();

is a variable of type functions or at least that is what you expect (see comments, the correct definition would be functions f;. As it is now, this would be the declaration of a function taking no arguments and returning an object of type functions).

The second one here:

for(int f = 1; f<4; f++){

is of type int.

The for loop is in a different scope than the where the first declaration is (each {} introduces a new scope) and therefore it is allowed to reuse identifiers for different objects.

If you refer to the doubly-used name, it will be looked up by certain rules and in the most common case the one in the most-inner scope will be used. Therefore here

cout << f.modu18()(y); //returns 0 or 1 from func

f is the loop counter of type int, not the f declare in the outer scope.

Use different variable names to solve this issue.

Additional stuff unrelated to error message:

1. Your function modu18 is supposed to return a string, but all your return statements return integer literals which are of integer type and can not be automatically cast to std::string, or rather the implicit conversion will not do what you expect it to.




2. You do not need classes to use multiple files. In a header file you can declare a free function with string modu18(int); and then define it in the implementation file with string modu18(int a) { ... }.




3. Using using namespace std; is not good practice, as it will lead to very hard to understand errors down the line. Especially in header files it should never be used. Instead specify all names from the standard library fully with std::.