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Fix Complex number custom formatting for negative imaginary parts #46897

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merged 5 commits into from
Jun 23, 2025

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@Copilot Copilot AI commented Jun 19, 2025

The ComplexFormatter examples in the documentation were producing incorrect output when formatting complex numbers with negative imaginary parts. Instead of displaying 12 - 15i, they would show 12 + -15i.

Problem

The custom formatter always used a hardcoded " + " operator between the real and imaginary parts:

// C# - Before
return c1.Real.ToString(fmtString) + " + " + c1.Imaginary.ToString(fmtString) + "i";

// VB.NET - Before  
Return c1.Real.ToString(fmtString) + " + " + c1.Imaginary.ToString(fmtString) + "i"

When c1.Imaginary was negative, ToString() would include the negative sign, resulting in output like "12 + -15i" instead of the expected "12 - 15i".

Solution

Updated both C# and VB.NET versions to:

  1. Calculate the appropriate sign based on the imaginary part's value
  2. Use Math.Abs() to get the absolute value of the imaginary part
  3. Display the calculated sign separately
// C# - After
char sign = c1.Imaginary < 0 ? '-' : '+';
return c1.Real.ToString(fmtString) + " " + sign + " " + Math.Abs(c1.Imaginary).ToString(fmtString) + "i";
' VB.NET - After
Dim sign As Char = If(c1.Imaginary < 0.0, "-"c, "+"c)
Return c1.Real.ToString(fmtString) + " " + sign + " " + Math.Abs(c1.Imaginary).ToString(fmtString) + "i"

Test Results

  • Positive imaginary: 12 + 15i ✅ (unchanged)
  • Negative imaginary: 12 - 15i ✅ (fixed from 12 + -15i)
  • Zero imaginary: 12 + 0i ✅ (unchanged)

The fix applies to both 'I' and 'J' formatting cases and maintains backward compatibility for positive and zero imaginary parts.

Fixes #46422.


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…matting issue

Co-authored-by: gewarren <24882762+gewarren@users.noreply.github.com>
Co-authored-by: gewarren <24882762+gewarren@users.noreply.github.com>
@Copilot Copilot AI changed the title [WIP] Example fails with a negative Imaginary part of a Complex. Fix Complex number custom formatting for negative imaginary parts Jun 19, 2025
Copilot finished work on behalf of gewarren June 19, 2025 16:41
@Copilot Copilot AI requested a review from gewarren June 19, 2025 16:41
…rget framework

Co-authored-by: gewarren <24882762+gewarren@users.noreply.github.com>
@Copilot Copilot AI requested a review from gewarren June 19, 2025 17:55
Copilot finished work on behalf of gewarren June 19, 2025 17:55
Co-authored-by: gewarren <24882762+gewarren@users.noreply.github.com>
@Copilot Copilot AI requested a review from gewarren June 19, 2025 18:00
Copilot finished work on behalf of gewarren June 19, 2025 18:00
@gewarren gewarren marked this pull request as ready for review June 23, 2025 12:24
@gewarren gewarren requested a review from a team as a code owner June 23, 2025 12:24
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@BillWagner BillWagner left a comment

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This LGTM @gewarren

Let's :shipit:

@gewarren gewarren merged commit 0c43c35 into main Jun 23, 2025
10 checks passed
@gewarren gewarren deleted the copilot/fix-46422 branch June 23, 2025 17:06
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Example fails with a negative Imaginary part of a Complex.
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