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Selection (if-then-else)

Selection (if-then-else). Programming Has 3 Types of Control: Sequential (normal) : Control of Execution Proceeds One after the Other Selection (if-then-else) : Control Proceeds Dependent on Conditions Iteration (looping) : Control Repeated until Condition Met. JAVA if Statement Syntax.

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Selection (if-then-else)

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  1. Selection (if-then-else) • Programming Has 3 Types of Control: Sequential (normal): Control of Execution Proceeds One after the Other Selection (if-then-else): Control Proceeds Dependent on Conditions Iteration (looping): Control Repeated until Condition Met

  2. JAVA if Statement Syntax • Syntax if (condition)statement; • If Condition Is True, Statement Is Executed • If Condition Is False, Statement Is Not Executed • If Multiple Actions Are Required for Statement, a Compound Statement Must Be Used: if (condition) { statement; statement; }

  3. Conditional Operators • Relational Operators: < , > , >= , <= • Equality Operators: == , != • NOTE: Cannot use Equality Operators with Strings; must Use .equals() : if (lastName.equals(“Li”))…

  4. Selection Examples if (age < 30) System.out.println( “You are very very Young”); if (grade == ‘A’) System.out.println(“Congratulations!” ); if (grade != ‘F’) System.out.println(“You passed!” ); if (studentName.equals(“No Student”)) System.out.println(“Student Not Registered”);

  5. else Statement • Syntax: • if (condition) • { • statement(s);//condition true • } • else • { • statement(s);//condition false • }

  6. if-else Example • if (myGrade >= 60) • { • System.out.println(“You passed!” ); • } • else • { • System.out.println(“How about them Cubs?” ); • }

  7. Compound Statements • Compound Statement: One or More Statements within a Set of Curly Braces • Must Use Compound Statement if More than One Statement Is Supposed to be under Control of if or else Conditional • Include Curly Braces after if so if other Statements Are Added in Future, Curly Braces Are Already There

  8. Nested if Statements if (myGrade >= 80) if (myGrade >= 90) System.out.println(“You have an A!” ); else System.out.println(“You have a B!” ); else System.out.println(“We’ll give you a C.” );

  9. if/else (Cascaded) • Sequence of if/else Statements • Example: if (myGrade > 90) System.out.println(“You have an A!” ); else if (myGrade > 80) System.out.println(“You have a B!” ); else if (myGrade > 70) System.out.println(“You have a C!” ); else System.out.println(“Oh-oh!” );

  10. Boolean Type • A Boolean Value Is One of Either “True” or “False” • In JAVA, Type boolean • Example: boolean done = false; . . . if (currentLetter == ‘Z’) done = true; . . . • if/else Conditionals Must Evaluate to True or False, and Are Therefore Called Boolean Expressions

  11. Logical Operators • A Logical Operator Is One Used to Further Specify True or False in an Expression • Connects Two or More Expressions Together • && Is Logical “AND” • || Is Logical ‘OR” • &&: Both Operands Must Be True for Entire Expression to Be True • ||: Only One (or Both) of the Operands Must Be True for Entire Expression to Be True

  12. Logical Operators if (numStudents > MIN && numStudents < MAX) classRun = true; if (numStudents > MAX || numInstructors == 0) classRun = false;

  13. Operator Precedence • () • ! (not) • *, /, % • +, - • <, <=, >, >= (Relational Operators) • ==, != (Equality Operators) • && (Logical AND) • || (Logical OR) • = (ASSIGNMENT)

  14. Order of Operations • Precedence: Level of Importance of Operations Multiplicative Operators Have Higher Precedence than Additive Operators: *, /, % Higher +, - Lower • Associativity: Order of Operation for Equal Level Precedence Most Operators Have Left-to-Right Associativity Use Parentheses to Force Differing Precedence of Operations

  15. Multiple Logical Operators if ( num1 > MAX || num2 == 0 && num3 == 0) System.out.println(“ num1 is MAX or something is 0”); System.out.println(“ I think…..” );

  16. Switch Statements • Also Called Switch/Case Statement • Just Case in Other Languages • Selects Among Several Different Actions • Can Only Select from Integer or Character • If an Integer Value Is Matched, Statements under Control of that Case Block Are Executed

  17. Switch/Case Example int numPassengers; System.out.print(“ Enter Passengers: “); numPassengers = scan.nextInt(); switch(numPassengers) { case 2: rate = BASERATE * 0.80; break; case 4: rate = BASERATE * 0.75; break; case 5: rate = BASERATE * 0.55; break; default: rate = BASERATE; break; }

  18. Switch Case Example char menuItem; String inputS; System.out.print("Enter Menu Selection: “); inputS = scan.next(); menuItem = inputS.charAt(0); switch(menuItem) { case 'O': case ‘o’: //Code to Order Something break; case 'C': case ‘c’: //Code to Checkout break; default: //Error Code break; }

  19. Announcements • Exam 1 Next Week Thursday • Everything through Lab 5 • 50 minutes • 15 % of Total Grade • Covers Everything through Lecture this Week • Quiz 1 Topics (terminology, variables, constants, basics) • if-then-else • Compound statements • Relational operators • Logical operators • Switch/Case Statements

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