An intro to programming The basic nittygritty thatll
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 (0 s and 1 s 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 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. PROGRAM CONTROL STATEMENT MISCELLANEOUS OUTPUT INPUT CALCULATION BASED ON INPUT OUTPUT PROGRAM CONTROL STATEMENT program Dog. Years; write “How old are you? ”; let human. Age = INPUT; let dog. Age = human. Age * 7; write human. Age; end program;
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 Dog. Years; write “How old are you? ”; let human. Age = INPUT; let dog. Age = human. Age * 7; write human. Age; 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 program Graduation; write “What grade did you just complete? ”; let last. Grade = INPUT; let years. Left = 12 – last. Grade; write last. Grade; 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 false int for integers char for letters double for real numbers string 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.
Graduation in Java import extra. *; public class Graduation { Java blather that’s meaningless for now public static void main(String args[]) { Std. out. println( "What grade did you just complete? " ); Write this: int last. Grade; Make a new variable of type int and call it “last. Grade” last. Grade = Std. in. read. Int(); Assign to “last. Grade” the value that the user inputs…hope it’s an integer int years. Left; Make a new variable of type int and call it “years. Left” years. Left = 12 - last. Grade; Use calculations to assign “last. Grade” a value based on “years. Left” Std. out. println( "You have " + years. Left + " years of high school left. "); } }
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 fave. Letter; int days; double food. Mass; 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: fave. Letter = ‘q’; days = 42; food. Mass = 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 fave. Letter = ‘q’; int days = 42; double food. Mass = 33. 42; string name = “Matthew”;
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. read. Int() reads an integer read. Char() reads a character read. Line() reads a string etc…
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. read. Int(); String name; Std. out. println(“What is your name? ) Name = Std. in. read. Line();
An exercise Write a program that: • Calculates the number a miles has traveled during the last year • Calculates the car’s 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
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 miles. Per. Day; miles. Per. Day = Std. in. read. Double(); Std. out. println( “How many gallons of gas did you use last year? ” ); int gallons. Used; gallons. Used = Std. in. read. Double(); double total. Miles = miles. Per. Day * 365; double avg. MPG = total. Miles / gallons. Used; Std. out. println( "You drove “ + total. Miles + “ miles last year and averaged “ + “ avg. MPG + “ miles per gallon. ”); } }
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
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