programming fundamentals

PROGRAMMING FUNDAMENTALS

Neal Stublen

nstublen@jccc.edu

APPLICATIONS AND DATA

What's a class?

A class is comprised of a set of data and the actions taken on that data

Each action is represented by a method A method is a set of statements that

performs a specific task Program execution will begin in a “main”

method

What's an identifier?

An identifier is a name we give to a class or method

No whitespace - spaces, tabs, line breaks, etc.

Not a keyword - words reserved by the programming language

Most likely case-sensitive, so "count" is not the same as "Count"

Identifier "Casing"

UPPERCASE lowercase PascalCase or UpperCamelCase lowerCamelCase Each language typically has its own

style for casing

Examples

Pseudocode

class Hello    main()        output "Hello”    returnendClass

Examples

Java

public class Hello{    public static void main(String[] args)    {        System.out.println("Hello");    }}

Examples

C#

public class Hello{    static void Main()    {        System.Console.WriteLine("Hello");    }}

What's a variable?

Data resides in the computer's memory A variable names the data stored at a

specific location in the computer's memory

Computer programs use variables to access and modify data stored in memory

What's a literal constant? Data that doesn't change is a constant Fixed values that appear in a computer

program are called literals or literal constants

Examples

input myNumber

myAnswer = myNumber * 2

myAnswer = myAnswer + 42

output myAnswer

myNumber is a variablemyAnswer is a variable2 is a literal constant42 is a literal constant

Examples

myName = "John Smith"

output myName

myName is a variable“John Smith” is a literal constant

Data Types

Numeric typesIntegerFloating point

String types Casting converts between data types

Variable Declaration

Variables are declared with a data type Variables are initialized with a value

num myNumber

num myNumber = 12

string myName

string myName = "John"

Named Constants

Variables can refer to values that are fixed

area = 3.14159265 * radius * radius

circumference = 2 * 3.14159265 * radius

Named Constants

Variables can refer to values that are fixed

num PI = 3.1415926

area = PI* radius * radius

circumference = 2 * PI* radius

Uninitialized Variables

Initialization places a known value into the memory location represented by a variable

Without initialization, the contents of a memory location could be anything

Typically called garbageAnd the source of many headaches

Assignment

Assign values to variables Assign using a literal constant Assign using another variable or

expression In some languages assignment can only

be performed between matching types

Examples

a = 1 // ‘a’ now has the value ‘1’

b = a // ‘b’ now has the value ‘1’

c = a + b // ‘c’ now has the value ‘2’

num a = 1

string name = “John”

name = a // Not allowed

Arithmetic Operations

Addition, + Subtraction, - Multiplication, * Division, / Modulus, %

Precedence Multiplication and division precede addition

and subtraction Parentheses are evaluated from the inside

out 2 + 3 * ( ( 4 + 5 ) / 3 + 1 ) 2 + 3 * ( 9 / 3 + 1 ) 2 + 3 * ( 3 + 1 ) 2 + 3 * 4 2 + 12 14

Good Practices Use code comments to clarify what is intended Choose identifiers that are clear Variable names are typically nouns (things,

e.g. radius) Method names typically combine a verb and

noun (act on a thing, e.g. calculateArea) Code that is easily readable can become self-

documenting What's clear now may not be clear later or

clear to someone else

Searching for something? a = w * l area = width * length

aTmp = 98.6 avgTemp = 98.6 averageTemperature = 98.6

crntSpd currentSpeed

ct cnt count

Readability

employeename employeeName employee_name

getTestComplete isTestComplete

Spacing and Line Breaks

Use consistent spacing and line breaks Indentation can show structure

class Circle

calculateArea

apply area formula

return

endClass

Use Temporary Variables

Break complex algorithms down into component parts

total = subtotal * (1 - discountRate) * (1 + taxRate)

discount = subtotal * discountRatediscountedTotal = subtotal - discountsalesTax = dscountedTotal * taxRatetotal = discountedTotal + salesTax

Write Clear Prompts

Calculation error. The starting balance is not valid.

Comment First, Code Second

Alternative to pseudocode and flowcharting

Stub out a class or method Write comments to document what

should happen within a method “Rewrite” the comments as code

Example

fillContactList()

{

// Retrieve contacts from a database

// Sort contacts by last name

// Add each contact to the contact list

}

Programming Structures

Sequence structurePerforms a series of actions in order

Selection structurePerforms one action or sequence or another

action or sequence based on a decision Loop structure

Repeats an action or sequence

Review

What is the value of:

8 – 4 * 6 / 4( 8 – 4 ) * 6 / 48 – 4 * ( 6 / 4 )

Exercise

Case Projects, p. 61, #1

Summary

Classes Identifiers Variables Data types Arithmetic operations and precedence Good practices Programming structures