C++硬币钱包程序作业指导：Coin结构体与Purse类设计需求

Got it, let's walk through how to approach this design—since you're asking for guidance rather than a full copy-paste solution, I'll break down the key pieces you need to focus on.

First, your Coin needs two core pieces of data: a name (like "US Quarter" or "Euro Cent") and a monetary value. Since we're dealing with currency, use decimal instead of float/double—floating-point types have precision issues that can mess up money calculations.

Key Requirements for Coin: #

• A constructor to initialize the name and value (add validation here! Don't allow empty names or negative values).
• A way to check if two Coins are equal (both name and value must match).

Guidance on Equality Check:

Instead of just writing a custom method, implement the IEquatable<Coin> interface—it's type-safe and avoids unnecessary boxing. Don't forget to override GetHashCode() too, since equal objects must have the same hash code (critical if you use Coin as a key in a dictionary later).

Here's a skeleton to build on:

public struct Coin : IEquatable<Coin>
{
    public string Name { get; }
    public decimal Value { get; }

    public Coin(string name, decimal value)
    {
        // Add validation: name can't be null/empty, value can't be negative
        if (string.IsNullOrWhiteSpace(name))
            throw new ArgumentException("Coin name can't be empty.", nameof(name));
        if (value <= 0)
            throw new ArgumentOutOfRangeException(nameof(value), "Coin value must be positive.");

        Name = name;
        Value = value;
    }

    // Type-safe equality check
    public bool Equals(Coin other)
    {
        // Compare both name and value for equality
        return string.Equals(Name, other.Name, StringComparison.OrdinalIgnoreCase) 
               && Value == other.Value;
        // Note: Use OrdinalIgnoreCase if you want "Quarter" and "quarter" to be the same—adjust based on your needs
    }

    // Override base Equals to handle non-Coin objects
    public override bool Equals(object obj)
    {
        return obj is Coin coin && Equals(coin);
    }

    // Override GetHashCode to match Equals logic
    public override int GetHashCode()
    {
        return HashCode.Combine(Name, Value);
    }

    // Optional: Overload == and != operators for cleaner code
    public static bool operator ==(Coin left, Coin right)
    {
        return left.Equals(right);
    }

    public static bool operator !=(Coin left, Coin right)
    {
        return !left.Equals(right);
    }
}

Your Purse needs to store a collection of Coins along with their quantities. The best choice here is a Dictionary<Coin, int>—it lets you quickly look up if a Coin already exists in the purse, so you can either add a new entry or increment the quantity.

Core Requirements for Purse: #

• An empty constructor to initialize the internal storage.
• A method to add a specified number of a given Coin.

Guidance on the Add Method:

• Validate the input quantity: it must be a positive integer (no adding zero or negative coins!).
• Check if the Coin is already in the dictionary: if yes, add the quantity to the existing count; if no, create a new entry.

Here's a skeleton for the Purse:

public class Purse
{
    // Internal storage: key = Coin, value = number of that coin in the purse
    private readonly Dictionary<Coin, int> _coinInventory;

    // Empty purse constructor
    public Purse()
    {
        _coinInventory = new Dictionary<Coin, int>();
    }

    // Method A: Add specified quantity of a Coin
    public void AddCoins(Coin coin, int quantity)
    {
        // Validate quantity first
        if (quantity <= 0)
            throw new ArgumentOutOfRangeException(nameof(quantity), "You must add a positive number of coins.");

        // Check if the coin is already in the purse
        if (_coinInventory.ContainsKey(coin))
        {
            _coinInventory[coin] += quantity;
        }
        else
        {
            _coinInventory.Add(coin, quantity);
        }
    }

    // Optional: Add helper methods to extend functionality
    public decimal GetTotalValue()
    {
        decimal total = 0;
        foreach (var (coin, count) in _coinInventory)
        {
            total += coin.Value * count;
        }
        return total;
    }

    public int GetCoinCount(Coin coin)
    {
        _coinInventory.TryGetValue(coin, out int count);
        return count;
    }
}

Extra Tips to Consider: #

• Thread Safety: If your Purse will be used in multi-threaded code, add locks around dictionary operations to prevent race conditions.
• Serialization: If you need to save/load the purse state, mark the Coin struct and Purse class as serializable (or use JSON serialization libraries like Newtonsoft.Json).
• Error Handling: Add more specific exceptions or validation as needed (e.g., what if someone tries to add a null Coin?).

内容的提问来源于stack exchange，提问作者anon001