Computer Science 101 Introduction to Programming

From Algorithms to Programs Algorithms are abstract things that can have –Linguistic realizations (in pseudocode or a programming language) –Hardware realizations (in digital circuitry)

What Is a Program? One or more algorithms written in a programming language that can be run on hardware Sometimes called software

What Is a Programming Language? A bit like pseudocode, but very strict syntax rules Examples: FORTRAN, COBOL, Lisp, Basic, C, C++, Java, Python, …

From Algorithms to Hardware Algorithm Program Circuitry Translate by human being Translate by compiler

The Program Development Process Editor Compiler Circuitry Program in programming language Program in machine language InputOutput Syntax errors

Python Free, general purpose programming language Can run code interactively in a shell Can also edit and run longer code segments called scripts or programs

Pattern of Simple Programs Get inputs from the user Run an algorithm on these inputs Print the results as outputs

Basic Elements: Variables Variable names - a sequence of letters and/or digits, can include _ (the underscore) Case sensitive - radius and Radius name two distinct variables Variables are usually spelled with lowercase letters, constants with uppercase letters

Assignment Statement Gives a variable a value Variables must have values before they are used in expressions PI = 3.14 area = PI * 6 ** 2 print area = = means set

Basic Elements: Keywords Keywords are special names reserved for special purposes print, if, else, while, import, … Color coded in orange in IDLE

Functions Run a computation on a given value to produce a new value The given values are called arguments >>> abs(-45) 45 >>> round(3.1416, 3) (, …, )

Numeric Data Types int - whole numbers, such as 45, 100, -20 float - numbers with a decimal point, such as 3.14, , -0.33

Arithmetic Operators +, -, *, /, %, ** Evaluate from left to right, but do ** first, the *, /, %, then +, - Use parentheses to override the standard order of evaluation / and % produce integer quotient and remainder with two int s, or a float when at least one operand is a float

Numerical Input The user is prompted with a text message The sequence of keystrokes is converted to an int or a float length = input("Enter the length: ") width = input("Enter the width: ") = input( ) input is a function

String Data Type Use " or ' as delimiters for simple strings Use """ as delimiters for multiline strings or comments """ File: rectangle.py Author: Ken """ length = input("Enter the length: ")

Output Statements print outputs numbers or strings Outputs a newline by default print "My name is Ken" print "I have 15 students" print

Output Statements Use a comma to print several data values on the same line, separated by a space name = "Ken" number = 15 print "My name is", name print "I have", number, "students"

Input of Text (Strings) The user is prompted with a text message The sequence of keystrokes is converted to a single string name = raw_input("Enter your name: ") color = raw_input("Enter your hair color: ") = raw_input( ) raw_input is a function

For Monday Homework due!