TheAlgorithms/C-Sharp · error · ArgumentOutOfRangeException

Capacity must be greater than 0

Error message

Capacity must be greater than 0

What it means

The HashTable constructor validates its parameters: capacity <= 0 throws ArgumentOutOfRangeException(nameof(capacity), "Capacity must be greater than 0"), and loadFactor <= 0 is rejected similarly. Capacity must be a positive integer because the table allocates bucket storage of at least that size (typically the next prime).

Solutions

1. Pass a positive capacity, e.g. new HashTable<K,V>(100).
2. Omit the parameter to use DefaultCapacity instead of passing 0.
3. Clamp before constructing: capacity = Math.Max(1, requestedCapacity).

Example fix

// before
var capacity = config.ExpectedEntries ?? 0; // 0 -> throws
var table = new HashTable<string, int>(capacity);
// after
var capacity = Math.Max(1, config.ExpectedEntries ?? DefaultCapacity);
var table = new HashTable<string, int>(capacity);

static bool IsValidCapacity(int capacity) => capacity > 0;
// call: if (!IsValidCapacity(cap)) cap = DefaultCapacity;

static bool IsPositive(int v) => v > 0;

try { var t = new HashTable<K,V>(cap, lf); }
catch (ArgumentOutOfRangeException ex) when (ex.ParamName == "capacity") { var t = new HashTable<K,V>(); }

When it happens

Trigger: new HashTable<K,V>(capacity: 0), new HashTable<K,V>(-5), or a capacity computed from input/config that is zero or negative.

Common situations: Config files with unset numeric fields defaulting to 0, computing capacity as expectedCount - removed where removed >= expectedCount, or passing 0 intending 'use default'.

Related errors

• k must be at least 1.
• Invalid block size
• Not enough space in input array for padding
• Vertex indices must be within valid range.
• Double factorial is only defined for non-negative integers…

AI-assisted analysis of TheAlgorithms/C-Sharp@96e2905cab (2026-09-13). Data as JSON: /api/errors/65dc6e40a0360010. Report an issue: GitHub.

Appendix: source

Thrown at DataStructures/Hashing/HashTable.cs:95

    /// <summary>
    /// Initializes a new instance of the <see cref="HashTable{TKey, TValue}"/> class.
    /// </summary>
    /// <param name="capacity">Initial capacity of the hash table.</param>
    /// <param name="loadFactor">Load factor of the hash table.</param>
    /// <exception cref="ArgumentOutOfRangeException">Thrown when <paramref name="capacity"/> is less than or equal to 0.</exception>
    /// <exception cref="ArgumentOutOfRangeException">Thrown when <paramref name="loadFactor"/> is less than or equal to 0.</exception>
    /// <exception cref="ArgumentOutOfRangeException">Thrown when <paramref name="loadFactor"/> is greater than 1.</exception>
    /// <remarks>
    /// <paramref name="capacity"/> is rounded to the next prime number.
    /// </remarks>
    /// <see cref="PrimeNumber.NextPrime(int, int, bool)"/>
    /// <see cref="PrimeNumber.IsPrime(int)"/>
    public HashTable(int capacity = DefaultCapacity, float loadFactor = DefaultLoadFactor)
    {
        if (capacity <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(capacity), "Capacity must be greater than 0");
        }

        if (loadFactor <= 0)
        {
            throw new ArgumentOutOfRangeException(nameof(loadFactor), "Load factor must be greater than 0");
        }

        if (loadFactor > 1)
        {
            throw new ArgumentOutOfRangeException(nameof(loadFactor), "Load factor must be less than or equal to 1");
        }

        this.capacity = PrimeNumber.NextPrime(capacity);
        this.loadFactor = loadFactor;
        threshold = (int)(this.capacity * loadFactor);
        entries = new Entry<TKey, TValue>[this.capacity];
    }

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