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Selection and Decision Making in Computer Science

Learn about selection and decision making in computer science, including conditional statements, boolean expressions, and complex decision-making processes. Develop correct decision-making programs using if statements, multiple selection, and the switch statement.

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Selection and Decision Making in Computer Science

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  1. CSC141 Computer Science I Zhen Jiang Dept. of Computer Science West Chester University West Chester, PA 19383 zjiang@wcupa.edu

  2. Selection (Decision) • Introduction • T/F selection • MC selection

  3. Selection (Decision) • Rolling a dice. • Sample execution (click on this link to try • http://www.cis.temple.edu/~jiang/dice.exe • Each button in the above sample has

  4. No Yes Win/Lost? Double the money Bankrupt Restart

  5. If else statement if (test) action 1 (statements 1) else action 2 (statements 2) //end if action 3 (statement 3)

  6. No Yes Test by boolean expression Action 1 Action 2 Action 3

  7. Boolean expression in test • Simple expression • Format <Value> <relational operators> <Value> • Number value relational operators, Table 3-1, page 111 ==, !=, <, >, <=, >= !!! Number one error: “(a=2)” instead of “(a==2)” • char value (not string!) relational operators ==, != (page 118)

  8. Complex expression • &&, ||, ! (Table 3-4, page 135) • Truth table • Table 3-6, page 136 • Table 3-7, page 139 • Table 3-8, page 141 • Precedence order, table 3-10, page 142 • Number range, page 142-143

  9. Development of a correct decision program • Grade.java

  10. Development Process • Identify two exclusive options • Implement each handling in different action parts • Identify the situation (values) for option selection • Make an expression so that all the situation value for option part 1 will lead to the test result (boolean value) true. • Verify all the situation value for option part 2 will lead to the test false, otherwise, revise the above expression!

  11. 60, 61, 62, …, 100 ? 1, 2, …, 58, 59

  12. Exercises 6 and 7, development of a correct decision program

  13. If statement, Code 3-1, page 113 • Relational operator ?, page 151 • Multiple selection • Nested if, Code 3-4, page 127 • If else if, Code 3-5, page 131 • Example: letter grade

  14. Comments: • Nested if for multiple selection problem If case 1 Else if case 2 else … //end of case 2 if //End of case 1 if

  15. Development of a correct multiple-decision program • Letter grade

  16. Exercise 8

  17. Switch • Switch([variable]) • Case [constant value]: • Break (or no break), Code 3-13, 3-14, page 155-157

  18. Project 2 • 11 case • If-else • BMI expression simplification • Last else no if • Nested if and multiple if • Avg < 90 && test1 < 90 to attend the final • Discount • %, ()?

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