---
title: ExcelConverter
summary: API reference for ExcelConverter.
status: draft
owner: <owner>
last_reviewed: 2026-07-23
library: SAIF.Framework.BaseN
reference_type: package
---

# ExcelConverter

`ExcelConverter` is a concrete `ConverterBase` subclass that represents base 26 using Excel-style, bijective spreadsheet column-letter semantics (A, B, … Z, AA, AB, …, with no zero digit). It overrides `Base`, `ConvertNumericToAlpha`, `ConvertAlphaToNumeric`, and `FormatBaseN`.

## Purpose
- Provide an `IConverter` implementation that reproduces Excel/spreadsheet-style column naming for base-26 conversion.*

## Context
- Namespace: `SAIF.Framework.BaseN`
- Assembly/package: `SAIF.Framework.BaseN` (also bundled into the `SAIF.BOF.Framework` NuGet package)

## Public members
| Member | Signature | Purpose |
| --- | --- | --- |
| `Base` | `Public Overrides ReadOnly Property Base() As Integer` | Returns `26`. |
| `ConvertNumericToAlpha` | `Public Overrides Function ConvertNumericToAlpha(ByVal input As Integer) As String` | Maps `1`–`26` to `"A"`–`"Z"` via `Chr(64 + input)`; throws `ConverterException` if `input > Base` ([BR-002](../../business-rules.md#br-002-excel-base-26-digit-must-not-exceed-base-26)). |
| `ConvertAlphaToNumeric` | `Public Overrides Function ConvertAlphaToNumeric(ByVal input As String) As Integer` | Accepts single characters only; numeric input passes through; letters mapped via `Asc(input.ToUpper) - 64`, bounds-checked against `Base`, throwing `ConverterException` if exceeded ([BR-002](../../business-rules.md#br-002-excel-base-26-digit-must-not-exceed-base-26)). Returns `-1` if input length is not 1.* |
| `FormatBaseN` | `Public Overrides Function FormatBaseN(ByVal values As Integer()) As String` | Renders a digit array right-to-left, applying bijective base-26 carry logic: a zero digit is replaced with `26` and the preceding digit is decremented/rolled, so no digit position ever renders as "0" ([BR-003](../../business-rules.md#br-003-excel-style-base-26-conversion-is-bijective-no-zero-digit)). |

## Behavioral notes
- `FormatBaseN` mutates the input `values` array in place while resolving carries (rollover) between digit positions.*
- `ConvertAlphaToNumeric` returns `-1` for multi-character or empty input rather than throwing, which differs from the single-character assumption used elsewhere in the type.*

## Constraints and usage notes
- Callers must catch `ConverterException` when passing potentially out-of-range digit values.
- Input to `ConvertAlphaToNumeric` is expected to be a single character; multi-character input yields `-1` rather than an exception.*

> **Note:** Statements marked with * were inferred from code structure, naming conventions, or
> contextual evidence where direct confirmation was not available in source artifacts. Statements
> marked with ** could not be confirmed; treat as unknown until verified. Statements marked with
> † were retrieved from dependency library documentation via the Legends CLI RAG service. They
> describe inherited behavior from the indicated origin library and should be verified if the
> dependency version changes.

## Sources
- `SAIF.Framework.BaseN\ExcelConverter.vb`
- `SAIF.Framework.BaseN\ConverterBase.vb`
- `SAIF.Framework.BaseN\ConverterException.vb`