Need help with this loop displaying only negative numbers.

[degausser]

These are the guidelines:

c= 3 + 10*k - k*k

Here are the two functions:

CrackCypher - this will contain the loop
CheckAnswer - this will check whether the value of k produces a negative value

Make sure that check answer returns a bool value, and takes an integer input.
Crack Cypher should return an integer as well.

You should determine what integer value of k makes the cypher negative.

And this is my code thus far:

#include <iostream>

int CrackCypher (int Guess);
bool CheckAsnwer(int c);

using namespace std;

int main()
{
    int Guess;
    CrackCypher(Guess);
}

bool CheckAsnwer(int c)
    {
        int k;

        c = 3 + (10*k) - (k*k);
        return c;
    }


int CrackCypher (int Guess)
    {
        for (int k = 0; k < 21; k++)
        {
            int c;
            int CheckAnswer(c);

            if (c < 0)
            {
                cout << c;
            }
        }
    }

I can do this perfectly fine without having to use functions, but since we have to use functions I have problems 'translating' it.
This is the code without using functions:

#include <iostream>

using namespace std;

int main()
{
    int c;

    for (int k = 0; k < 21; k++)
        {
            c = 3 + (10*k) - (k*k);
            if (c < 0)
            {
                cout << c;
            }
        }
}

Help please?

[vlad from moscow]

I think that in this function

bool CheckAsnwer(int c)
    {
        int k;

        c = 3 + (10*k) - (k*k);
        return c;
    }

variables shall be transposed as

bool CheckAsnwer(int k)
    {
        int c;

        c = 3 + (10*k) - (k*k);
        return c;
    }

[degausser]

I tried that, but I still get nothing in return on the console.
I feel like my logic is wrong somewhere, but I'm not seeing it. :\