Introduction

Code review is the process where one or more developers examine another developer’s code before it becomes part of the main project.

In real software development, writing code is not the final step. Before code is merged, deployed, or released, it should be reviewed to check correctness, readability, maintainability, security, testing, and alignment with project standards.

A good code review helps the whole team learn, reduces mistakes, improves software quality, and creates shared ownership of the codebase.

Easy Real-Life Example

Essay Review:
- Check spelling
- Check grammar
- Check clarity
- Check missing points

Code Review:
- Check bugs
- Check logic
- Check readability
- Check test cases
- Check security
- Check maintainability

Code review works like proofreading, but for software code.

What is Code Review?

Code review is a quality-checking practice where code changes are inspected before they are accepted into the main codebase.

The reviewer reads the code, checks whether it solves the intended problem, verifies whether it follows coding standards, and gives feedback if improvements are needed.

Why Code Review is Important

Code review is important because even experienced developers can miss bugs, edge cases, or design problems in their own code.

A second pair of eyes can catch problems early before they become production defects.

Who Participates in Code Review?

Code review usually involves two main roles: the author and the reviewer.

Common Code Review Workflow

A simple code review workflow usually follows these steps.

1. Developer writes code
2. Developer tests the code
3. Developer creates a pull request or merge request
4. Reviewer checks the code
5. Reviewer gives feedback
6. Developer makes improvements
7. Reviewer approves the code
8. Code is merged into the main branch

This workflow helps teams review changes before they become part of the shared codebase.

What is a Pull Request?

A pull request, often called a PR, is a request to merge code changes from one branch into another branch.

The pull request usually contains the changed files, description, comments, test results, and review discussion.

Pull Request Contains:
- Title
- Description
- Changed files
- Reason for change
- Test information
- Reviewer comments
- Approval or requested changes

What Reviewers Should Check

A reviewer should focus on important quality areas instead of only checking formatting.

Simple Code Review Checklist

Responsibilities of the Code Author

A code author should make the review easy for reviewers.

Responsibilities of the Reviewer

A reviewer should give useful feedback that improves the code and helps the author.

Giving Constructive Feedback

Code review feedback should be clear, polite, and useful.

The goal is to improve the code, not to criticize the person.

Example: Code Review Comment

Code Submitted

FUNCTION calc(m)
    IF m >= 40 THEN
        RETURN "P"
    ELSE
        RETURN "F"
    END IF
END FUNCTION

Review Feedback

Suggestion:
Can we rename calc to calculateResult and m to marks?
Also, returning "Pass" and "Fail" instead of "P" and "F"
will make the output more readable.

Improved Code

FUNCTION calculateResult(marks)
    IF marks >= 40 THEN
        RETURN "Pass"
    ELSE
        RETURN "Fail"
    END IF
END FUNCTION

The improved code is easier to understand because names and outputs are clearer.

Code Review vs Testing

Code review and testing are both important, but they are not the same.

Automated Checks in Code Review

Automated tools can support code review by checking common issues before human review.

Automated Checks May Include:
- Formatting check
- Linting
- Unit tests
- Build verification
- Code coverage
- Static analysis
- Security scanning

Automated checks help reviewers focus more on logic, design, and maintainability instead of only style issues.

Keep Code Reviews Small

Small and focused code reviews are easier to understand and more effective.

Large reviews are harder to inspect properly and may cause reviewers to miss important issues.

Security in Code Review

Code review should also consider security risks.

Student-Friendly Example: Grade Calculator Review

Requirement:
Create a function that returns grade based on marks.

Review Checklist:
- Does the function handle marks below 0?
- Does the function handle marks above 100?
- Are boundary values checked?
- Are names meaningful?
- Is the code readable?
- Are test cases written for 40, 60, 75, 90?
- Are invalid inputs handled clearly?

Real-World Example: E-Commerce Checkout Review

Best Practices for Code Review

Common Beginner Mistakes

Prerequisites Before Learning Code Review

Students should understand the following topics before learning code review deeply:

Trace Table Example: Code Review Process

Practice Activity: Review the Code

Review the following pseudocode and suggest improvements.

FUNCTION calc(m)
    IF m >= 40 THEN
        RETURN "P"
    ELSE
        RETURN "F"
    END IF
END FUNCTION

Sample Review Suggestions

1. Rename calc to calculateResult.
2. Rename m to marks.
3. Return "Pass" and "Fail" instead of "P" and "F".
4. Add validation for marks below 0 or above 100.
5. Add unit tests for 40, 39, 0, 100, and invalid values.

Improved Version

FUNCTION calculateResult(marks)
    IF marks < 0 OR marks > 100 THEN
        RETURN "Invalid marks"
    ELSE IF marks >= 40 THEN
        RETURN "Pass"
    ELSE
        RETURN "Fail"
    END IF
END FUNCTION

Mini Quiz

Interview Questions on Code Review Basics

Quick Summary