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Lab 0

Professor Sprenkle sprenkles@wlu.edu September 11, 2007. Lab 0. Objectives. Why programming languages? Start lab #0 UNIX/Linux Portal account (Blog for “Broader CS Issues”) Web page Text Editor Python. Why Do We Need Programming Languages?. Computers can’t understand English

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Lab 0

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  1. Professor Sprenkle sprenkles@wlu.edu September 11, 2007 Lab 0

  2. Sprenkle - CS111 Objectives Why programming languages? Start lab #0 UNIX/Linux Portal account (Blog for “Broader CS Issues”) Web page Text Editor Python

  3. Sprenkle - CS111 Why Do We Need Programming Languages? • Computers can’t understand English • Too ambiguous (PB&J) • Humans can’t easily write machine code Problem Statement (English) Machine code/Central Processing Unit (CPU) 000000 0000100010 00110 00000 100000

  4. Sprenkle - CS111 Programmer (YOU!) translates from problem to algorithm (solution) to program Python interpreter translates into bytecode Why Do We Need Programming Languages? • Computers can’t understand English • Too ambiguous (PB&J) • Humans can’t easily write machine code Problem Statement (English) Algorithm/Pseudocode High-level Programming Language (Python) Bytecode Machine code/Central Processing Unit (CPU)

  5. Sprenkle - CS111 Why Do We Need Programming Languages? • Computers can’t understand English • Too ambiguous (PB&J) • Humans can’t easily write machine code Problem Statement (English) Algorithm/Pseudocode High-level Programming Language (Python) Python interpreter executes the bytecode in a “virtual machine” Bytecode Machine code/Central Processing Unit (CPU)

  6. Sprenkle - CS111 Python Is • A programming language • An interpreter (a program)

  7. Sprenkle - CS111 Have a lot of these early on! Python Interpreter • Validates the Python programming language expression • Enforces Python syntax • Reports syntax errors • Simulates a computer (executes the expression) Python expression Interpreter (python) Only if no syntax errors Output Executable bytecode

  8. Sprenkle - CS111 Have a lot of these early on! Python Interpreter • Validates the Python programming language expression • Enforces Python syntax • Reports syntax errors • Simulates a computer (executes the expression) • Runtime errors (e.g., divide by 0) • Semantic errors (not what you meant) Python expression Interpreter (python) • Good way to test expressions Output Executable bytecode

  9. Sprenkle - CS111 Our Programming Process Programmer types a program/script into a text editor(jEdit or IDLE). An interpreter turns each expression into bytecode and then executes each expression Program text file program.py Text Editor (jEdit or IDLE) Interpreter (python) 1 “line” at a time • Get feedback about which line caused the problem • Interpreter stops validating/executing lines Output Executable bytecode

  10. Sprenkle - CS111 Lab 0 • Start on paper --> Web, after log in • Linux worksheet • Login • Open browser • Navigate to Lab 0, from “Schedule” page • Continue on Web-based Lab 0

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