声明一个 C++ 类

Question

I am struggling knowing how to create a class. I want to create a "Player" class and all I want to do is pass in the name while I'll have the other variables start at 0 until they are updated when a game is run (later in the program)

Player::Player(string name_in)    
{
    name = name_in;
    int numOfWins = 0;
    int numOfLoses = 0;
    int numOfDraws = 0;
    int totalMatches = 0;
}

Right now there are lots of errors around numOfWins, numOfLoses, numOfDraws and totalMatches. What can I do to fix this?

Answer 1

Perhaps the error is in your int ... part of assignments, which essentially creates a new local variable in a constructor.

Try this version:

#include <string>
using namespace std;

class Player
{
    string name;
    int numOfWins;
    int numOfLoses;
    int numOfDraws;
    int totalMatches;

public:
    Player(string name_in)    
    {
        name = name_in;
        numOfWins = 0;
        numOfLoses = 0;
        numOfDraws = 0;
        totalMatches = 0;
    }
};

Answer 2

The errors you get, at least from the snippet you posted are caused for you can't declare variables in constructor - you declare them in class body and initialize in constructor or using another function.

#include <string>

class Player {
public:
    Player( std::string const& name_in) : name( name_in),
                                          numOfWins(), numOfLoses(),
                                          numOfDraws(), totalMatches()
                                          {}  // constructor 
                                              // will initialize variables
                                              // numOfWins() means default 
                                              // initialization of an integer
private:
    std::string name;
    int numOfWins;
    int numOfLoses;
    int numOfDraws;
    int totalMatches;
};

usage:

int main() {
    Player( "player_one");
    return 0;
}

Answer 3

You should declare other instance variables in the class declaration, rather than declaring them as locals (which is completely useless).

// This part goes in the header
class Player {
    string name;
    int numOfWins;
    int numOfLoses;
    int numOfDraws;
    int totalMatches;
public:
    Player(string name_in);
};

Now in the constructor you could use initialization lists:

// This part goes into the CPP file
Player::Player(string name_in)
// Initialization list precedes the body of the constructor
: name(name_in), numOfWins(0), numOfLoses(0), numOfDraws(0), totalMatches(0) {
// In this case, the body of the constructor is empty;
// there are no local variable declarations here.
}

Answer 4

Kinda vague, but I'll take a crack at it. You Probably want:

class Player{
    string name;    
    int numOfWins;
    int numOfLosses;
    int numOfDraws;
    int totalMatches;
    Player(string name_in)
};

Player::Player(string name_in){
    name = name_in;
    numOfWins = 0;
    numOfLosses = 0;
    numOfDraws = 0;
    totalMatches = 0;
}

Haven't used C++ in a while, so this may be faulty.