1. CS-1010 Dr. Mark L. Hornick 1 Selection and Iteration and conditional expressions

2. CS-1010 Dr. Mark L. Hornick 2 Instructions in a Java program are executed in sequence Starting with the first instruction in your main() method and continuing to the end. To alter the control flow, decision-making instructions can be added to a program An instruction that alters the control flow is called a control statement or selection statement. public static void main(…) … }

3. CS-1010 Dr. Mark L. Hornick 3 The Java if statement specifies whether a block of code should execute …depending on the result of evaluating a test condition called a boolean expression public static void main(…) { if( ){ // block of code that executes when // the boolean expression is true } }

4. CS-1010 Dr. Mark L. Hornick 4 What is a boolean expression? First recall: A numerical expression uses arithmetic operators and is evaluated to a numerical value Some numerical expressions using binary arithmetic operators: x+y x-y x*y x/y Arithmetic operators operate on numerical datatypes byte, short, int, long, float, double Exception: (+ operator works for the String datatype)

5. CS-1010 Dr. Mark L. Hornick 5 The boolean datatype is another primitive datatype Variables declared as boolean datatypes can only assume one of the two boolean values: true false boolean isOK = false; boolean insufficientFunds = true; boolean, true, and false are Java reserved words

6. CS-1010 Dr. Mark L. Hornick 6 A boolean expression uses relational operators between numerical values and is evaluated to a boolean value: either true or false. x < y// less than operator; evaluates to true if x is less than y; otherwise false x <= y// less than or equal to; note =< is not valid x > y// greater than x >= y// greater than or equal to x == y// equal to; be careful w.r.t. x=y x != y// not equal to

7. CS-1010 Dr. Mark L. Hornick 7 Variables of data type boolean can be declared and assigned to the result of a boolean expression: int score = 86; boolean result; result = 70 < score; if ( result ){ … }

8. CS-1010 Dr. Mark L. Hornick 8 The { } braces are optional, but this means that the block of code is the single instruction following the if statement if ( ) // executed if true // executed always This means that whatever Java statement following the if statement will be executed when the boolean expression is true And only the single instruction following the if(…)

9. CS-1010 Dr. Mark L. Hornick 9 Methods can be declared to return a boolean value The String class has a contains() method that returns a boolean result: String message = “Welcome to MSOE”; boolean isPresent = message.contains(“to”); if( isPresent ) // contains “to” JOptionPane.showInputDialog(…);

10. CS-1010 Dr. Mark L. Hornick 10 A more complex if statement if ( ){ // executed when exp. is true } else { }// executed when exp. is false The else clause is optional When present, the instructions in the else block are executed only when the boolean expression is false

11. CS-1010 Dr. Mark L. Hornick 11 The Boolean operators Repeat: relational operators take numerical operands and return a boolean value: either true or false. Example: (x<y) Exception: == and != operators can be used between boolean datatypes A boolean operator takes boolean values as its operands and returns a boolean value. The three boolean operators are &&// means “and” ||// means “or” !// means “not”

12. CS-1010 Dr. Mark L. Hornick 12 Boolean operators and their meanings: PQP && QP || Q!P false true falsetruefalsetrue false truefalse true false

13. CS-1010 Dr. Mark L. Hornick 13 Complex boolean expressions int x = 100, t=50; boolean passed, record; // initialized to false passed = (x >= 70); // or !(x < 70) record = (t = 60) if( pass && record ) msg = “You passed in record time!”;

14. CS-1010 Dr. Mark L. Hornick 14 Complex boolean expressions int x = 100, t=50; boolean pass, record; // initialized to false pass = (x >= 70); // evaluates to true record = (t < 60); // evaluates to true boolean both = pass && record; if( both ){ msg = “You passed in record time!”; } // always safer to include { }

15. SE-1010 Dr. Mark L. Hornick 15 Looping and Repetition Statements control a block of code to be executed for: a fixed number of times 1, 10, 10000… until a certain condition is met a value remains positive (or negative) a value remains below (or above) some limit …

16. SE-1010 Dr. Mark L. Hornick 16 The two (three) main loop types: while() and it’s cousin do…while() Sentinel-controlled loops, where the loop body is executed repeatedly until a designated condition, called a sentinel, is encountered. for() A count-controlled loop, where the loop body is executed a fixed number of times.

17. SE-1010 Dr. Mark L. Hornick 17 The do-while() Statement Format: do { } while ( ); The part is known as the loop body The loop body is executed until the becomes false And is always executed at least once! Even if is false

18. SE-1010 Dr. Mark L. Hornick 18 The do-while() statement Demo

19. SE-1010 Dr. Mark L. Hornick 19 The while Statement Format: while ( ){ // 0 or more } As long as the is true, the loop body is executed

20. SE-1010 Dr. Mark L. Hornick 20 JOptionPane Confirmation dialog Created by using the showConfirmDialog method of the JOptionPane class: int answer = JOptionPane.showConfirmDialog(null, “Play another game?", “Confirmation", JOptionPane.YES_NO_OPTION, JOptionPane.QUESTION_MESSAGE); // answer will contain the values corresponding // to JOptionPane.YES_OPTION or JOptionPane.NO_OPTION