I know that there are a lot of questions somewhat related to this one, but they answers are a bit hard for me to make sense of. I'm receiving the following error for a few different lines of code:

C:\Users\Jeff\AppData\Local\Temp\ccAixtmT.o:football.cpp:(.text+0x6f0): undefined 
reference to `Player::set_values(int, std::string, float)'

From these blocks of code:

class Player {
int playerNum;
string playerPos;
float playerRank;
public:
    void set_values(int, string, float);
    float get_rank(){ return playerRank; };
    bool operator == (const Player &p1/*, const Player &p2*/) const
    {
    if(&p1.playerNum == &playerNum &&
       &p1.playerPos == &playerPos &&
       &p1.playerRank == &playerRank)
       return true;
    else
       return false; };
};

And this being the main function referencing the subclass:

int main() {

ifstream infile;
infile.open ("input.txt", ifstream::in);
int numTeams;
string command;
while(!infile.fail() && !infile.eof()){
    infile >> numTeams;
    string name;
    Player p;
    int playNum;
    string playPos;
    float playRank;
    Player all[11];
    float ranks[11];
    Team allTeams[numTeams];
    for(int i=0; i<numTeams; i++){
        infile >> name;
        for(int j=0; j<11; j++){
            infile >> playNum;
            infile >> playPos;
            infile >> playRank;
            if(playPos == "QB")
                p.set_values(playNum, playPos, (playRank*2.0));
            else if(playPos == "RB")
                p.set_values(playNum, playPos, (playRank*1.5));
            else if(playPos == "WR")
                p.set_values(playNum, playPos, (playRank/1.8));
            else if(playPos == "TE")
                p.set_values(playNum, playPos, (playRank*1.1));
            else if(playPos == "GD")
                p.set_values(playNum, playPos, (playRank/2.0));
            else if(playPos == "TC")
                p.set_values(playNum, playPos, (playRank/2.2));
            else if(playPos == "CR")
                p.set_values(playNum, playPos, (playRank/1.2));
            all[j] = p;
            allTeams[i].set_values(all, name);
        }
    }
    infile >> command;
    if (command == "play"){ 
        int t1;
        int t2;
        infile >> t1;
        infile >> t2;
        play(allTeams[t1], allTeams[t2]); 
    }
    else { 
        int t1;
        int p1;
        int t2;
        int p2;
        swap(allTeams[t1], allTeams[t1].get_player(p1), allTeams[t2], allTeams[t2].get_player(p2)); }
}
}