Code Complexity: What It Is & How to Measure It

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Rafael Timbó
Rafael Timbó
Chief Technology Officer
Code Complexity: What It Is & How to Measure It

Table of Contents

Learning how complex a software program or system's coding is a very general explanation of code complexity. Here's the full definition, and how to measure the complexity to determine quality.
Published on
August 18, 2023
Updated on
November 6, 2023

Measuring code complexity is essential to software engineering as it helps evaluate a codebase's maintainability and reliability. In addition, it provides you with valuable insights into the code's structural and design elements, allowing you to identify areas that may be prone to bugs or require improvement.

Learn more about code complexity, how its measured, code complexity metrics, and more.

What Is Code Complexity?

Code complexity is the extent to which a software program or system is challenging to understand, maintain, and modify. It measures how hard it is to understand a program's logic, structure, and organization and how much effort is required to make changes. Code complexity can arise from many factors, including the size of the codebase, the number of modules and dependencies, the depth of nesting and inheritance, and the use of complex algorithms and data structures.

High code complexity can make fixing bugs, adding new features, or changing a program challenging. Even minor modifications can have unintended consequences and be difficult to debug. As a result, developers use code complexity to determine the quality and maintainability of software and make efforts to minimize it wherever possible.

Importance of Measuring Code 

Measuring code complexity helps improve software quality, maintainability, and performance. Code complexity impacts the following elements of software:

  • Maintainability: High complexity makes it difficult to understand, modify, and maintain code, leading to increased development costs and a longer time to market.
  • Debugging: Complex code is often harder to debug, as it can be challenging to understand how changes to one part of the code will impact other functions. By measuring code complexity, developers can identify code prone to bugs and take steps to simplify it and reduce the risk of bugs.
  • Quality: Code complexity is often an indicator of code quality. High complexity can make it difficult to write unit tests and verify that the code works as intended, leading to poor code quality.
  • Performance: Complex code can also impact performance, as complex algorithms and data structures can lead to slower execution times.

How to Measure Code Complexity

Code complexity measurements are subjective and can vary depending on the context and perspective of the person evaluating it. As such, it's a good idea to use a combination of metrics and analysis techniques to understand the code's complexity.

  1. Define the scope: Determine which portions of the code you want to analyze, such as individual functions or entire modules.
  2. Choose a metric or metrics: There are several ways to measure code complexity, including examining the number of branches, the depth of nested constructs, and the amount of code involved.
  3. Collect data: Use tools or manual methods to gather data on the code you're measuring. Measuring could include counting the number of lines of code, tracking the number of decisions or branches in the code, or measuring the indentation level of the code.
  4. Analyze the data: Evaluate the data you have collected to determine the complexity of the code. Some methods include calculating metrics, such as the average cyclomatic complexity of a function, or simply making a subjective judgment about the code's readability and maintainability.
  5. Report the results: Present the results of your analysis clearly and concisely, highlighting areas of the code that are particularly complex or difficult to understand.

Code Complexity Metrics

Code complexity analysis metrics are quantitative measures that help assess the difficulty level in understanding and maintaining a software system. These metrics can be based on various factors, such as the number of branches in the code, the depth of nested constructs, and the amount of code involved. Some metrics may also consider the functional aspects of the code, such as the number of inputs and outputs or the frequency of certain types of constructs.

These metrics represent the code's complexity, making it easier to compare and analyze different parts of a software system. You can combine several metrics to understand the code's complexity and identify overly complex code.

Lines of Source Code

Lines of source code (LOC) is a simple and straightforward metric for measuring the size of a software system. It's calculated by counting the number of lines of code in the source files of a program. This metric shows the amount of code involved in a project and compares the size of different software systems.

Maintainability Index

The Maintainability Index is a composite metric that provides a single number score indicating the maintainability of a software system. It's based on several factors that impact the ease of understanding and maintaining code, including cyclomatic complexity, comment density, and lines of code.

The Maintainability Index is calculated using a formula that considers these various factors and generates a score that ranges from zero to 100, with higher scores indicating a higher level of maintainability. A score of 100 represents the highest level of maintainability, while a score of zero represents the lowest level.

Cyclomatic Complexity

Cyclomatic complexity is a software metric used to measure the complexity of a program. It quantitatively measures the number of independent code paths in a program's source code. It determines the number of test cases required to test a program thoroughly.

Analyzing the cyclomatic complexity of a program can be calculated using the program's control flow graph. In this graph, each node represents a basic block of code, and each edge represents a possible flow of control from one basic block to another. The cyclomatic complexity is then defined as the number of edges minus the number of nodes plus two.

Cyclomatic complexity indicates the difficulty of understanding and maintaining a program and identifies areas of code that may be particularly prone to bugs and errors. A higher cyclomatic complexity value indicates a more complex program and, therefore, a higher risk of bugs and errors.

Rework Ratio

The rework ratio is a software metric that measures the amount of work being redone or reworked — also called code churn — in a software development project. It's calculated as the ratio of the total time spent on fixing defects and making changes to the total time spent on development.

The rework ratio is an important metric because it provides insight into the efficiency of the software development process. For example, a high rework ratio can indicate that the development process could be more efficient, as a significant amount of time and resources are spent fixing defects and making changes.

Halstead Volume

Halstead Volume is a software metric that measures the size and complexity of a program.

The Halstead Volume metric is based on the number of distinct operators and operands used in a program and the number of times each operator and operand is used. The metric calculates a value that represents a program's total volume of information.

You can use Halstead Volume to compare the complexity of different programs or to track the evolution of the complexity of a single program over time. You can also use it to identify areas of code that may be particularly prone to bugs and errors.

Using Metrics to Predict Defect Probability 

Measuring the right code metrics is a proven method of accurately predicting defect probability. By focusing on metrics such as code complexity, maintainability index, and code coverage, software developers and quality assurance teams can make informed decisions about the potential for defects in their code. The right code metrics are powerful tools for ensuring successful software development.

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