1 / 22

Introduction to Programming with Java, for Beginners

Introduction to Programming with Java, for Beginners. Control Structures. Sequential Control Flow. Consists of just a list of commands to be done in order Welcome to Dr. Java > int x = 2; > int squareOfX = x * x; > System.out.println(x); //Or just type: squareOfX 2.

red
Download Presentation

Introduction to Programming with Java, for Beginners

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript


  1. Introduction to Programmingwith Java, for Beginners Control Structures

  2. Sequential Control Flow • Consists of just a list of commands to be done in order Welcome to Dr. Java > int x = 2; > int squareOfX = x * x; > System.out.println(x); //Or just type: squareOfX 2

  3. What are control Structures ? • You can’t do very much if your program consists of sequential control flow • The program cannot choose whether or not to perform a command • The program cannot perform the same command more than once • Such programs are extremely limited! • Control structures allow a program to base its behavior on the values of variables

  4. Recap: Boolean • Boolean is one of the eight primitive types • Booleans are used to make yes or no decisions • All control structures use Booleans • There are exactly two Boolean values, true (“yes”) and false (“no”) • Boolean, true, and false are all lowercase • Boolean variables are declared like any other kind of variable: • Booleanhungry; • booleanpassingGrade; • booleantaskCompleted= false;

  5. Numeric & Boolean Comparisons • The following comparisons each give a Boolean result: (25 > 24) && (12 == 13) //results tofalse (25 > 24) || (12 == 13) //results totrue

  6. Conditionals (“if” statements) • An “if” statement is a flow control statement • It is also called a conditional, or a branch • We’ll see several “flavors” • An “if” all by itself • An “if” with an “else” part • An “if” with an “else if” part

  7. “if” statement if (condition){ statement(s) } If the condition is true, then the statement(s) (i.e. instructions) will be executed. Otherwise, it/they won’t.

  8. “if-else” statement

  9. Cascading “if-else”

  10. Nested if-statements

  11. The infamous “dangling else” • An else is paired with the last else-less if, regardless of spacing, unless { } dictate otherwise.

  12. A “Loop” • A simple but powerful mechanism for “making lots of things happen!” • Performs a statement (or block) over & over • Usually set up to repeat an action until some condition is satisfied, e.g. • Run an application until user hits “quit” button • Read characters until end of file reached • Deal card hands until game over

  13. Syntax of the while statement • condition is a true/false (boolean) expression • If condition is initially false, the statement is never executed • If condition is true, statement is executed and condition is re-evaluated • The statement should eventually make the loop stop while (condition){ statement(s) }

  14. A while Loop to Print Numbers // Print the numbers 1 thru 10 int x = 1; while (x <= 10){ System.out.println(x); x = x + 1; }

  15. AnInfinite Loop // Faulty attempt to print 1 thru 10 int x = 1; while (x <= 10){ System.out.println(x); }

  16. More Infinite Loops // Some infinte loops are intentional while (true){ statement(s) } // Others are not int x = 5; while (x < 10){ statement(s) which don’t change x }

  17. Pseudocode and Loops Pseudocode is an informal, english-like, code-like way Of sketching out what you want your code to do. initialize game while( the game isn’t over){ process player input update game state determine if game should end } if game should be saved save game quit

  18. Compute Square of first 10 numbers //In Square.java int number = 1; int squareOfNumber = 0; while (number <= 10) { squareOfNumber = number * number; System.out.println(number + " " + squareOfNumber); number = number + 1; }

  19. For Loop for (init; end-test; re-init){ statement } • Executes loop body as long as end-test evaluates to TRUE • Initialization and re-initialization code included in loop statement • Note: Test is evaluated before executing loop body

  20. While vs. For Note: For loops are used generally for bounded iteration

  21. Summary of Loops

  22. Indentation • if(x<10){___x=x+1;} else{___x=x-1;} • while(x>0){___System.out.println(x);___x=x-1;} • Recommended indentation is from 2 to 4 spaces, but must be consistent throughout the program • Most important style rule: If you are modifying or adding to an existing program, keep to the original style (whatever it may be)

More Related