Lesson 2: The Way of the Program: Let's Start Programming

• Overview
  • Natural vs. Formal language
  • Rules of Syntax
  • Debugging
  • First program
• Natural Language
  • Spoken by people (English, Hebrew, Spanish)
  • Ambiguous
    • “Give me the thing”, “Oh, sure.”, “Great!”
  • Redundant
  • Filled with idioms (not literal)
    • “I could eat a cow”, “You’re killing me”, “Go fly a kite”
• Formal Language
  • Man-made
    • Math, Chemistry, Computer Programming
  • Unambiguous
    • 1+4=5
    • CH₄ + 2O₂ --> 2H₂O + CO₂
    • Print “Hello world”;
  • Concise
  • Literal
• Languages have rules of Syntax
  • Tokens
    • Basic elements (letters, words, symbols)
    • Good Tokens: 1+3=4 ; CAT; H₂O
    • Bad Tokens: 2@+#=!; C€§; H_hO
  • Structure
    • The way tokens are arranged
    • Good Structure: 1+3=4; CAT; H₂O
    • Bad Structure: 13+=4; CTA; ₂HO
• Debugging
  • Errors in a program are called “bugs”
  • Debugging is the process of tracking down errors and fixing them
  • Debugging is one of the most important skills in programming
• Three main types of bugs:
  • Syntax Errors
    • Using a token or structure that is incorrect
    • Program will quit with an error message
  • Run-Time Errors
    • Error that occurs during execution
    • Program will quit running
  • Logic Errors
    • Error in how program is logically constructed
    • Program runs, but does wrong thing
• Python: Interpreter vs Scripting
  • Interpreter:
    • Immediate feedback
    • Code not saved
  • Scripting:
    • Code saved
    • Feedback delayed
    • More debugging required
• Scripting Basics
  • Type in “Idle”, Notepad, or text editor
  • Save as .py
  • To run:
    • Open a DOS command prompt
    • Navigate to the directory with the file
    • Type "yourfile.py”
• Review
  • What is the difference between a natural and formal language?
  • What are tokens and structure?
  • What are the three main types of bugs?
  • What is the difference between creating a Python script and working in the interpreter?
  • Use the Python interpreter to perform basic calculations.
  • Create 2 scripts in Python, one math, one “Hello world”