improve(docs): Basics -> Functions

[PoetaKodu]

Overview

Rework the lesson structure, split into sublessons (examples, exercises, etc.)

Functions

• Lesson structure
  • Motivation
  • Introduction
  • Creating functions
    • a basic example without parameters (a procedure)
    • with parameters
    • return statement
    • returning a value
    • Declaration and definition
  • Overloading (basics)
  • Summary
• 💡 Examples
  • calculate area of a circle
  • convert Fahrenheit to Celsius
  • calculate factorial of a number
  • average value of array of numbers
  • calculate gcd
  • calculate a power of a number (exponent is a positive integer)
  • reverse a string
  • check if a string is a palindrome
• 💢 Common problems
  • incorrect number or type of arguments
  • not returning a value
  • missing declaration
• 📚 Exercises
  • count occurrences of a character in a string
  • count number of vowels in a string
  • detect if string is an anagram
  • convert int to string