Difference Between 'const' and 'readonly' in C# — The Definitive, Practical Guide

📰 Dev.to · Libin Tom Baby

Learn the difference between 'const' and 'readonly' in C# to write more effective code

intermediate Published 18 Feb 2026
Action Steps
  1. Define a constant using 'const' to store a value that never changes
  2. Use 'readonly' to declare a variable that can be initialized only once
  3. Compare the IL behavior of 'const' and 'readonly' to understand compilation differences
  4. Evaluate performance notes to determine when to use each keyword
  5. Apply 'const' and 'readonly' in real-world scenarios to improve code quality
Who Needs to Know This

Software engineers and developers who work with C# will benefit from understanding the difference between 'const' and 'readonly' to make informed decisions in their code

Key Insight

💡 'const' is compile-time evaluated, while 'readonly' is runtime evaluated, affecting how and when to use each

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💡 Know when to use 'const' vs 'readonly' in C# to improve your code

Key Takeaways

Learn the difference between 'const' and 'readonly' in C# to write more effective code

Full Article

Learn the difference between const and readonly in C#. Includes definitions, IL behavior, performance notes, and real-world scenarios to choose the right one.
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