An intro to programming

1
An intro to programming

• The basic nitty-gritty thatll make you scratch
  your head and say, This is programming?

2
What is a program?

• A program is computer coding that
• Takes input
• Performs some calculation on the input
• Displays output

3
A program is a function!

• Both take inputs and give outputs based on some
  rule
• Both make calculations
• Both take arguments

4
A program is a NOT function!

• In a function, there is exactly one output for
  every input
• Some computer programs will have different
  outputs for the same input
• Example a virtual set of dice

5
The client

• The user of the program is sometimes called the
  client
• The client doesnt have to know whats going on
  inside the black box to use the program
• Do you know exactly how Microsoft Word works?

6
Using outside sources

• Many programs must consult outside sources to
  perform the correct calculations on their input

7
Writing programs

• You need
• Knowledge of a coding language
• A compiler translates your language into
  machine code (0s and 1s the computer can
  understand)

8
What is pseudocode?

• Pseudocode is programmers shorthand for actual
  code
• It mimics actual programming languages
• There are no rules of pseudocodeyet

9
A simple pseudocode program
A program that 1) asks the users age in human
years, 2) calculates the users age in dog years,
and 3) tells the user what that age is.

• program DogYears
• write How old are you?
• let humanAge INPUT
• let dogAge humanAge 7
• write humanAge
• end program

PROGRAM CONTROL STATEMENT ?
MISCELLANEOUS OUTPUT ?
INPUT ?
CALCULATION BASED ON INPUT ?
OUTPUT ?
PROGRAM CONTROL STATEMENT ?
10
A few good pseudocode rules

• The name of the program begins with a capital
  letter
• Each line ends in a semicolon
• All variable names begin in lowercase
• We use an asterisk () to represent
  multiplication (also use , -, /, )

• program DogYears
• write How old are you?
• let humanAge INPUT
• let dogAge humanAge 7
• write humanAge
• end program

11
Write your own pseudocode program

• Write a program in pseudocode that
• Asks the client what grade they just finished
• Calculates how many years of high school the
  client has remaining.
• Outputs this answer.

12
A sample program

• program Graduation
• write What grade did you just complete?
• let lastGrade INPUT
• let yearsLeft 12 lastGrade
• write lastGrade
• end program

13
Three parts of programs

• Variables, to store data
• Calculation statements, to handle input,
  calculations, and output
• A user interface, which allows the client to use
  the program

14
Variables primitive types

• Different types depending on the kind of data
• In Java, some types includeboolean for true or
  falseint for integerschar for lettersdouble
  for real numbersstring for strings
• These are called primitive types because they are
  built into the language

15
Variables - objects

• In some languages, including Java, users can
  define their own variable types, called objects
• An object is a collection of primitive types
• Example an object representing a cat might
  contain a double variable for its weight, a
  string variable for its name, and a boolean
  variable for if its been neutered or spayed

16
Variables - objects

• In some languages, including Java, users can
  define their own variable types, called objects
• An object is a collection of primitive types
• Example a string is an object that holds many
  char variables, so a string is any set of
  letters a word or a sentence

17
Java

• Java was released in 1995 by Sun Microsystems.
• It is based on the language C.
• Java is platform-independent, object-oriented,
  and easy to use on the Internet.

18
Graduation in Java

• import extra.
• public class Graduation
• public static void main(String args)
• Std.out.println( "What grade did you just
  complete?" )
• int lastGrade
• lastGrade Std.in.readInt()
• int yearsLeft
• yearsLeft 12 - lastGrade
• Std.out.println( "You have " yearsLeft "
  years of high school left.")

Write this
Make a new variable of type int and call it
lastGrade
Assign to lastGrade the value that the user
inputshope its an integer
Make a new variable of type int and call it
yearsLeft
Use calculations to assign lastGrade a value
based on yearsLeft
19
Declaring variables

• We create variables for our program to use by
  declaring them
• Declaring a variable is like saying, Computer,
  save some space in RAM for this variable
• Declaring is done ONCE before using the variable
• a variable does NOT assign a value to the variable

20
How to declare a variable

• Write the variables type
• Leave a space
• Write the variables name (start with a lowercase
  letter, its good style)

• Exampleschar faveLetterint daysdouble
  foodMassstring name

21
How to assign a value to a variable

• Write the variables name
• Write a single equals sign ()
• Use single quotes for char, double quotes for
  string
• Write the variables value and a semicolon

• ExamplesfaveLetter qdays 42foodMass
  33.42name Matthew

22
Declaring and assigning at the same time

• You can, if you choose, declare variables and
  assign values to them at the same time
• Write the variables type, then its name, and
  then its value
• Exampleschar faveLetter qint days
  42double foodMass 33.42string name
  Matthew

23
Input the easy way

• Because input in Java is not easy, we use a
  package called extra that assists with input.

• To input using extra
• Declare a variable
• Assign an input statement as its value
• The input statement should begin with
  Std.in.readInt() reads an integerreadChar()
  reads a characterreadLine() reads a stringetc

24
Output always easy

• To output, write Std.out.println()
• In the parens, write a variable name, a string,
  or any combination of variables and strings
  connected with plus () signs

25
Input and output examples

• int days
• Days Std.in.readInt()
• String name
• Std.out.println(What is your name?)
• Name Std.in.readLine()

26
An exercise

• Write a program that
• Calculates the number a miles has traveled during
  the last year
• Calculates the cars average miles/gallon
• You should ask the client for the average number
  of miles per day s/he drives and the total
  gallons of gas s/he uses in one year

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A solution

• import extra.
• public class Miles
• public static void main(String args)
• Std.out.println( How many miles per day do you
  drive?" )
• double milesPerDay
• milesPerDay Std.in.readDouble()
• Std.out.println( How many gallons of gas did
  you use last year? )
• int gallonsUsed
• gallonsUsed Std.in.readDouble()
• double totalMiles milesPerDay 365
• double avgMPG totalMiles / gallonsUsed
• Std.out.println( "You drove totalMiles
  miles last year and averaged avgMPG
  miles per gallon.)

28
Another exercise

• Write a program that
• Calculates the amount of change you should
  receive when you go shopping and the type of
  bills you should receive it in
• You should ask the client for the price of the
  article and the amount of cash s/he actually paid