[c++] How do I fix a "Expected Primary-expression before ')' token" error?

Here is my code. I keep getting this error:

error: expected primary-expression before ')' token

Anyone have any ideas how to fix this?

void showInventory(player& obj) {   // By Johnny :D
for(int i = 0; i < 20; i++) {
    std::cout << "\nINVENTORY:\n" + obj.getItem(i);
    i++;
    std::cout << "\t\t\t" + obj.getItem(i) + "\n";
    i++;
}
}

std::string toDo() //BY KEATON
{
std::string commands[5] =   // This is the valid list of commands.
    {"help", "inv"};

std::string ans;
std::cout << "\nWhat do you wish to do?\n>> ";
std::cin >> ans;

if(ans == commands[0]) {
    helpMenu();
    return NULL;
}
else if(ans == commands[1]) {
    showInventory(player);     // I get the error here.
    return NULL;
}

}

showInventory(player);     // I get the error here.

void showInventory(player& obj) {   // By Johnny :D

this means that player is an datatype and showInventory expect an referance to an variable of type player.

so the correct code will be

  void showInventory(player& obj) {   // By Johnny :D
    for(int i = 0; i < 20; i++) {
        std::cout << "\nINVENTORY:\n" + obj.getItem(i);
        i++;
        std::cout << "\t\t\t" + obj.getItem(i) + "\n";
        i++;
    }
    }

players myPlayers[10];

    std::string toDo() //BY KEATON
    {
    std::string commands[5] =   // This is the valid list of commands.
        {"help", "inv"};

    std::string ans;
    std::cout << "\nWhat do you wish to do?\n>> ";
    std::cin >> ans;

    if(ans == commands[0]) {
        helpMenu();
        return NULL;
    }
    else if(ans == commands[1]) {
        showInventory(myPlayers[0]);     // or any other index,also is not necessary to have an array
        return NULL;
    }

}