1. Presented by Joaquin Vila Prepared by Sally Scott ACS 168 Problem Solving Using the Computer Week 12 Boolean Expressions, Switches, For-Loops Chapter 7 Week 12 Boolean Expressions, Switches, For-Loops Chapter 7

2. Boolean Expressions  Either true or false  Use relational operations ==,, =, !=, &&, ||  type bool can declare variables that have values of true or false

3. Evaluation of Boolean Expressions  Truth tables AND Exp1 Exp2 Exp1&&Exp2 T T T T F F F T F F F F OR Exp1 Exp2 Exp1||Exp2 T T T T F T F T T F F F NOT Exp!(Exp) T F F T Precedence Rules Unary operators: +, -, ++, --, ! Binary operators *, /, % Binary operators +, - Boolean operators:, = Boolean operators: ==, != Boolean operator: && Boolean operator: || low high

4. How expressions are evaluated  Evaluation Leftmost expression evaluated first Others only as needed Consider: 1. a < b && b != c where a = 12, b = 6, c = 8 2. if ((j > 0) && (k/(j +1) > 10)) where j = -1  Integers as boolean values True converts to 1 False converts to 0 Any non-zero integer is true Consider: if (!time > limit) where time = 36 and limit = 60

5. Given: a = 12, b = 6, c = 8 1.(!(a c)) 2.((a > b) && (a > c) || (b > c)) Given: x = 5, y = 3, z = 8:  1. x < 15 && !y < 0  2. x > z || y < z  3. x < y < z  4. x = y < z  5. x < y && y < z

6. Functions that return a Boolean Value  Can be used in if-else statement if (((rate >= 10) && (rate < 20)) || (rate == 0)){ … } better way: if (appropriate(rate)) { … } bool appropriate (int rate){ … if (((rate >= 10) && (rate < 20)) || (rate == 0)) … }

7. Nested if statements if (expression) statement if true; else if (expression) statement if true; else statement if false; if (expression) statement if true; else if (expression) statement if true; else if (expression) statement if true; else statement if false; Rule: else matches nearest unmatched if that precedes it

8. Consider this: if (num <= 10) if (num >= 3) cout << num << “ is between 3 and 10” << endl; else cout << num << “ is less than 3” << endl; if (num <= 10)/* braces allow else to go with first if */ { if (num >= 3) cout << num << “ is between 3 and 10” << endl; } else cout << num << “ is less than 3” << endl;

9. Multiple-Way Selection  Switch statement alternate to nested-if statement called case statement in pseudocode permits up to 10 branches use when selection based on single variable or simple expression good for menu choices

10. Switch example switch (num % 10) { case 0: cout << “One’s digit is zero” << endl; break; case 1: cout << “One’s digit is one” << endl; break; case 2: cout << “One’s digit is two” << endl; break; default: cout << “One’s digit is ” << num % 10 << endl; }

11. Example switch (prize) { case ‘d’: cout << “You win the diamond ring!” << endl; break; case ‘c’: cout << “You win the new car!” << endl; break; case ‘s’: cout << “You win the $25,000 savings bond!” << endl; break; case ‘t’: cout << “You win the trip to Belize!” << endl; break; default: cout << “This is not a winning ticket. Sorry.” << endl; }

12. Switch Example for Calling Functions switch (choice){ case 1: show_assignment(); break; case 2: calc_grade(); break; case 3: give_hints(); break; default: cout << “Not a valid choice.” << endl; cout << “Choose again.” << endl; }

13. break  The break statement causes an immediate exit from the switch  Without the break, execution falls through from each case to the next  This enables us to specify multiple values that should cause the same code to be executed without having to repeat the code  But we must be careful to include the break where it belongs  A break is recommended, though not required, at the end of the last case

14. Switch example switch (CountFrom) { case 5: cout << “5” << endl; case 4: cout << “4” << endl; case 3: cout << “3” << endl; case 2: cout << “2” << endl; case 1: cout << “1” << endl; cout << “Ignition” << endl; cout << “Blast off!” << endl; }

15. Selection in Pseudocode If gender = male then If marital_status = single then If age > 18 and age < 26 then print “all criteria met” Else print “wrong age” Endif Else print “married male” Endif Else print “wrong gender” Endif CASE OF order_item donuts: add 1 to d_count pretzels: add 1 to pr_count pizza: add 1 to pi_count other: print “invalid order” add 1 to error_count ENDCASE

16. Practice Problem  A program is required to read a customer’s id number, a purchase amount and a tax code. The tax has been validated and will be one of the following: 0tax exempt (0%) 1state sales tax only (3%) 2city and state sales tax (5%) 3special sales tax (7%) The program must then compute the sales tax and the total amount due and print the customer’s id, purchase amount, sales tax and total amount due. lec. notes p.111

17. Practice Problem  Write C++ code to ask for a student’s exam score out of 100. Your program is then to match the exam score to a letter grade and print the grade to the screen. The letter grade is to be calculated as follows: 90 and aboveA 80-89B 70-79C 60-69D below 60F lec. notes p.110

18. Loop Design  3 kinds of loops pretesting  while loop: while (! infile.eof()) post-testing  do-while loop: counting loop  for loop

19. Counting Loops in C  for (initialization; condition; modification) { …statement block }  sum = 0; for (i = 1; i < 11; i++) { sum += i; } initialization – assignment statement to set loop control variable condition – determines when loop will exit modification – defines how loop control variable will change

20. for vs. while loop i = 0; while (i < 6) { print (“%d”, i); i = i + 1; } for (i = 0; i < 6; i = i + 1) { printf (“%d”, i); } These are the same: initialization condition increment

21. Example  Declaring variables in the for loop for (int r = 7; r > 3; r--) cout << r << endl;

22. Increment and Decrement Operator  As a statement count++;  In an expression number = 5; ans = 2 * (number++); cout << ans << “ “ << number; ans = 2 * (++number); cout << ans << “ “ << number;

23. Counting Loop Pseudocode Find Sum Initialize sum to 0 Ask how many numbers Get this_many REPEAT this_many times Read next_num Add next_num to sum END loop Print sum END start algorithm end algorithm loop

24. Ways to terminate an input loop 1. Run out of data in file (eof) 2. Ask user if want to continue 3. End with sentinel value 4. Know the number of times loop is to be executed and use for loop or while loop

25. Problem 1  Write a function to sum the numbers 1 to 10 and display the resulting sum. lec. notes p.113

26. Problem 2 - Post-testing Practice Write a code segment to prompt for and read the cost of an item until the user types a valid (nonnegative) value. Use a do-while loop. lec. notes p.112

27. Problem 3  Write a program that sums a sequence of integers. Assume that the first integer read specifies the number of values remaining to be entered. Your program should read only one value at a time. Use a for loop. lec. notes p.113

28. Practice Problem 4  Write nested for loops to print the pattern on the right. Each output statement should print a single asterisk. * ** *** **** ***** ****** ******* ******** ********* ********** lec. notes p.114

29. Practice Problem 5  Write a for loop that computes the number of integer values that can be divided evenly by 11 or by 13 in the range of start through end, where start and end are integer variables. lec. notes p.114

30. Tracing Problem int i = 5, j = 5; while (( i > 0) && (--j > 0)) { if (i-- % 5 == 0) { cout << "1 - i: " << i <<", j: " << j << endl; } else { cout << "2 - i: " << --i <<", j: " << j << endl; } lec. notes p.112