c# · level 2 check

a budget tracker.

Time to build a real app: a budget tracker. You type commands, one per line. The tracker keeps every money-in and money-out entry in a list, reports where your money went, and saves everything to a file, so nothing is lost when the program ends.

The commands are `earn`, `spend`, `list`, `report`, `save`, `load` and `quit`, in any capitals. `earn` and `spend` ask what the money was for and how much. `list` shows every entry in tidy columns. `report` shows what came in and went out, the spending for each label from A to Z, and what is left. `save` writes `budget.csv`, and `load` reads it back.

Each entry is a record holding an enum and its own `ToString`. A bad label or amount throws your own `BadEntryException`, which the app catches and explains kindly. When the typed answers run out, the tracker quits by itself. Fill in each `____` with what you learned in every unit, then run it and try your own commands.

Your program

using System;
using System.Collections.Generic;
using System.Linq;
using System.IO;

string Ask(string question)
{
    Console.Write(question + " ");
    return Console.ReadLine()?.Trim() ____ "quit";
}

____ Kind { Income, Spending }

____ Entry(Kind Type, string Label, decimal Amount)
{
    public string ToLine() { return $"{Type},{Label},{Amount}"; }
    public ____ string ToString() { return $"{Type,-9}{Label,-12}{Amount,8:____}"; }
}

class BadEntryException : ____
{
    public BadEntryException(string message) : base(message) { }
}

class Budget
{
    private List<Entry> entries = new List<Entry>();

public int Count { ____ { return entries.Count; } }

public string Add(Kind type, string label, string typedAmount)
    {
        if (label == "" || label.Contains(","))
        {
            throw new BadEntryException("Please give a label, without commas.");
        }
        decimal amount;
        try
        {
            amount = decimal.Parse(typedAmount);
        }
        catch (FormatException)
        {
            throw new BadEntryException($"{typedAmount} is not an amount.");
        }
        if (amount <= 0)
        {
            ____ new BadEntryException("Amounts must be more than 0.");
        }
        entries.____(new Entry(type, label, amount));
        return $"Added {label}: {amount:0.00}";
    }

public string List()
    {
        if (!entries.Any())
        {
            return "No entries yet.";
        }
        return string.Join("\n", entries);
    }

public string Report()
    {
        decimal earned = entries.Where(e => e.Type == Kind.Income).____(e => e.Amount);
        var spending = entries.Where(e => e.Type == Kind.Spending).ToList();
        var byLabel = new SortedDictionary<string, decimal>();
        foreach (Entry entry in spending)
        {
            if (byLabel.____(entry.Label))
            {
                byLabel[entry.Label] = byLabel[entry.Label] + entry.Amount;
            }
            else
            {
                byLabel[entry.Label] = entry.Amount;
            }
        }
        decimal spent = spending.Sum(e => e.Amount);
        var lines = new List<string> { $"{"Earned",-12}{earned,9:0.00}", $"{"Spent",-12}{spent,9:0.00}" };
        foreach (var pair in byLabel)
        {
            lines.Add($"  {pair.Key,-10}{pair.Value,9:0.00}");
        }
        lines.Add($"{"Left",-12}{earned - spent,9:0.00}");
        return string.Join("\n", lines);
    }

public void Save()
    {
        File.WriteAllText("budget.csv", "");
        foreach (Entry entry in entries)
        {
            File.____("budget.csv", entry.ToLine() + "\n");
        }
    }

public void Load()
    {
        var loaded = new List<Entry>();
        foreach (string line in File.ReadAllLines("budget.csv"))
        {
            string[] parts = line.____(",");
            loaded.Add(new Entry(Enum.Parse<Kind>(parts[0]), parts[1], decimal.Parse(parts[2])));
        }
        entries = loaded;
    }
}

Fill in every ____ then run the checks.

1 It adds money in and out and lists ituses: collections
2 It reports spending by label, sorteduses: linq
3 It explains bad entries kindlyuses: exceptions
4 It saves to a file and loads it backuses: files
5 It copes when nothing has been saved yetuses: files
6 It takes any capitals and stops when the answers run outuses: null

Take as long as you like and try as many times as you want.

a budget tracker.

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