What are the main principles that make code readable and easy to maintain?

Main principles that make code readable and easy to maintain:

• Clear names: variables, functions, and classes should have names that reflect their purpose.
• Simplicity and clarity: avoid unnecessary complexity, write code so that it is easy to understand at first glance.
• Breaking down into functions and modules: each function should perform a single task.
• Documentation: comments and docstrings help understand why a particular piece of code is needed.
• Following coding style: a consistent style makes reading and maintaining code easier.

Example in Python:

def calculate_area(radius):
    """Calculates the area of a circle based on the radius."""
    pi = 3.14159
    return pi * radius ** 2

Here, the function has a clear name, is short, and includes a description of what it does.