An intro to programming

The basic nitty-gritty that’ll make you scratch your head and say, “This is programming?”

What is a program?

• A program is computer coding that:

• Takes input• Performs some

calculation on the input

• Displays output

A program is a function!

• Both take inputs and give outputs based on some “rule”

• Both make calculations

• Both take “arguments”

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

The client

• The user of the program is sometimes called the client

• The client doesn’t have to know what’s going on inside the “black box” to use the program

• Do you know exactly how Microsoft Word works?

Using outside sources

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

Writing programs

• You need:• Knowledge of a

coding language• A compiler –

translates your language into machine code (0s and 1s the computer can understand)

What is pseudocode?

• Pseudocode is programmers’ shorthand for actual code

• It mimics actual programming languages

• There are no “rules” of pseudocode…yet

A simple pseudocode program

program DogYears;

write “How old are you?”;

let humanAge = INPUT;

let dogAge = humanAge * 7;

write humanAge;

end program;

INPUT

CALCULATION BASED ON INPUT

OUTPUT

MISCELLANEOUS OUTPUT

PROGRAM CONTROL STATEMENT

PROGRAM CONTROL STATEMENT

A program that 1) asks the user’s age in human years, 2) calculates the user’s age in dog years, and 3) tells the user what that age is.

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;

Write your own pseudocode program

Write a program in pseudocode that:

1. Asks the client what grade they just finished

2. Calculates how many years of high school the client has remaining.

3. Outputs this answer.

A sample programprogram Graduation;

write “What grade did you just complete?”;

let lastGrade = INPUT;

let yearsLeft = 12 – lastGrade;

write lastGrade;

end program;

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

Variables – primitive types

• Different types depending on the kind of data

• In Java, some types include:boolean 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

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 it’s been neutered or spayed

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

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.

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.");

}}

Graduation in Java

Java blather that’s meaningless for now

Write this:

Make a new variable of type int and call it “lastGrade”

Assign to “lastGrade” the value that the user inputs…hope it’s an integer Make a new variable of type int and call it

“yearsLeft”Use calculations to assign “lastGrade” a value based on “yearsLeft”

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

How to declare a variable

• Write the variable’s type

• Leave a space• Write the

variable’s name (start with a lowercase letter, it’s good style)

• Examples:

char faveLetter;int days;double foodMass;string name;

How to assign a value to a variable

• Write the variable’s name

• Write a single equals sign (=)

• Use single quotes for char, double quotes for string

• Write the variable’s value and a semicolon

• Examples:

faveLetter = ‘q’;days = 42;foodMass = 33.42;name = “Matthew”;

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 variable’s type, then its name, and then its value

• Examples:char faveLetter = ‘q’;int days = 42;double foodMass = 33.42;string name = “Matthew”;

Input: the easy wayBecause 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…

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

Input and output examples

int days;

Days = Std.in.readInt();

String name;

Std.out.println(“What is your name?)

Name = Std.in.readLine();

An exercise

Write a program that:• Calculates the number a miles has

traveled during the last year• Calculates the car’s average

miles/gallonYou 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

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.”);

}}

A solution

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