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Inventory audit

Validate product identifiers and quantities before accepting an import.

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All C# source files below are loaded together in the playground. Files written by a run live in its virtual directory.

Program.cs

using System;
using System.Linq;
using System.Collections.Generic;
using System.Globalization;
using System.Text;
using System.Text.Json;
using System.Threading;
using System.Threading.Tasks;

var rows = new[] { new Stock("A1", 3), new Stock("B2", 0), new Stock("A1", 8), new Stock("C3", -1) };
var errors = InventoryAudit.Validate(rows);
Console.WriteLine(errors.Length == 0 ? "Import ready" : string.Join("\n", errors));

Models/Stock.cs

public sealed record Stock(string Code, int Quantity);

Validation/InventoryAudit.cs

using System;
using System.Collections.Generic;
public static class InventoryAudit
{
    public static string[] Validate(IEnumerable<Stock> rows)
    {
        var seen = new HashSet<string>(StringComparer.Ordinal);
        var errors = new List<string>();
        var number = 0;
        foreach (var row in rows)
        {
            number++;
            if (string.IsNullOrWhiteSpace(row.Code)) errors.Add($"Row {number}: missing code");
            else if (!seen.Add(row.Code)) errors.Add($"Row {number}: duplicate {row.Code}");
            if (row.Quantity < 0) errors.Add($"Row {number}: quantity is negative");
        }
        return errors.ToArray();
    }
}

Inventoryaudit.csproj

<Project Sdk="Microsoft.NET.Sdk">
  <PropertyGroup>
    <OutputType>Exe</OutputType>
    <TargetFramework>net9.0</TargetFramework>
    <ImplicitUsings>enable</ImplicitUsings>
    <Nullable>enable</Nullable>
  </PropertyGroup>
</Project>