Programming (Ü) Flow of Control. Solutions

Transcription

1 Programming (Ü) Solutions

2 Exercise 1 Write an expression that evaluates to true if and only if the value of the integer variable x is equal to zero.

3 Exercise 1 Solution x == 0

4 Exercise 2 Write an expression that evaluates to true if the value x is greater than or equal to y.

5 Exercise 2 Solution x >= y

6 Exercise 3 Write an expression that evaluates to true if the value of the integer variable widthofbox is not divisible by the value of the integer variable widthofbook. Assume that widthofbook is not zero. ("Not divisible" means it has a remainder.)

7 Exercise 3 Solution widthofbox % widthofbook!= 0

8 Exercise 4 Given that the variables x and y have already been declared and assigned values, write an expression that evaluates to true if x is non-negative and y is negative.

9 Exercise 4 Solution x >= 0 && y < 0

10 Exercise 5 Clunker Motors Inc. is recalling all vehicles in its Extravagant line from model years Given a variable modelyear and a String modelname write a statement that prints the message "RECALL" to standard output if the values of modelyear and modelname match the recall details.

11 Exercise 5 Solution if((modelyear>=1999&&modelyear<=2002) &&modelname.equals("extravagant")) System.out.println("RECALL");

12 Exercise 6 Write a conditional that assigns 10,000 to the variable bonus if the value of the variable goodssold is greater than 500,000.

13 Exercise 6 Solution if (goodssold > ) bonus = 10000;

14 Exercise 7 Given the integer variables x and y, write a fragment of code that assigns the larger of x and y to another integer variable max.

15 Exercise 7 Solution if (x>y) max = x; else max = y;

16 Exercise 8 Write an if-else statement that outputs the word "High" if the value of the variable score is greater than 100 and outputs "Low" if the value of score is at most 100. The variable score is of type int.

17 Exercise 8 Solution if (score > 100) System.out.println("High"); else System.out.println("Low");

18 Exercise 9 Write an if/else statement that adds 1 to the variable minors if the variable age is less than 18, adds 1 to the variable adults if age is 18 through 64 and adds 1 to the variable seniors if age is 65 or older.

19 Exercise 9 Solutions if (age < 18) minors++; else if (age < 65) adults++; else seniors++;

20 Exercise 10 Suppose salary and deductions are variables of type double that have been given values. Write an if-else statement that outputs the word "Crazy" if salary is less than deductions; otherwise, it should output "OK" and set the variable net equal to salary minus deductions.

21 Exercise 10 Solutions if (salary < deductions) { System.out.println("Crazy"); } else { System.out.println("OK"); net = salary - deductions; }

22 Exercise 11 What output will be produced by the following code? int extra = 2; if (extra < 0) System.out.println("small"); else if (extra == 0) else System.out.println("medium"); System.out.println("large");

23 Exercise 11 Solutions large

24 Exercise 12 Write a multiway if-else statement that classifies the value of an int variable n into one of the following categories and writes out an appropriate message: n < 0 or 0 n < 100 or n 100 Hint: Remember that the Boolean expressions are checked in order.

25 Exercise 12 Solutions if (n < 0) System.out.println(n + " is less than zero."); else if (n < 100) else System.out.println(n + " is between 0 and 99 (inclusive)."); System.out.println(n + " is 100 or larger.");

26 Exercise 13 Suppose savings and expenses are variables of type double that have been given values. Write an if-else statement that outputs the word "Solvent", decreases the value of savings by the value of expenses, and sets the value of expenses to zero, provided that savings is larger than expenses. If, however, savings is less than or equal to expenses, the if-else statement should simply output the word "Bankrupt" without changing the value of any variables.

27 Exercise 13 Solution if (savings > expenses) { System.out.println("Solvent"); savings = savings - expenses; expenses = 0; } else { System.out.println("Bankrupt"); }

28 Exercise 14 Given an int variable k, use a while loop to print a single line consisting of 88 asterisks. Use no variables other than k.

29 Exercise 14 Solution k=1; while(k<=88) { System.out.print('*'); k++; } System.out.println();

30 Exercise 15 Given an int variable n that has been initialized to a positive value and, in addition, int variables k and total, use a while loop to compute the sum of the cubes of the first n whole numbers, and store this value in total. Use no variables other than n, k, and total and do not modify the value of n.

31 Exercise 15 Solution total=0; k=n; while(k>0) { total=total+k*k*k; k--; }

32 Exercise 16 Given an int variable n that has already been initialized to a positive value, use a do...while loop to print a single line consisting of n asterisks. Use no variables other than n.

33 Exercise 16 Solution do { System.out.print('*'); } while(--n>0); System.out.println();

34 Exercise 17 Given an int variable n that has been initialized to a positive value and, in addition, int variables k and total that have already been declared, use a do...while loop to compute the sum of the cubes of the first n whole numbers, and store this value in total. Use no variables other than n, k, and total.

35 Exercise 17 Solution total=0; k=n; do { total+=k*k*k; k--; } while(k>0);

36 Exercise 18 Given an int variable k that has already been declared, use a for loop to print a single line consisting of 97 asterisks. Use no variables other than k.

37 Exercise 18 Solution for(k=1; k<=97; k++) { System.out.print("*"); }

38 Exercise 19 Given int variables k and total that have already been declared, use a for loop to compute the sum of the squares of the first 50 counting numbers, and store this value in total. Thus your code should put 1*1 + 2*2 + 3* * *50 into total. Use no variables other than k and total.

39 Exercise 19 Solution total=0; for (k=1; k<=50; k++) { total+=k*k; }

40 Exercise 20 Assume that the int variables i and j have been declared, and that n has been declared and initialized. Using for loops (you may need more than one), write code that will cause a triangle of asterisks of size n to be output to the screen. * ** *** **** ***** ******

41 Exercise 20 Solution for(i=1;i<=n;i++) { for(j=1;j<=i;j++) { System.out.print("*"); } System.out.println(); }

42 Exercise 21 You have just purchased a stereo system that cost $1,000 on the following credit plan: no down payment, an interest rate of 18% per year (and hence 1.5% per month), and monthly payments of $50. The monthly payment of $50 is used to pay the interest, and whatever is left is used to pay part of the remaining debt. Hence, the first month you pay 1.5% of $1,000 in interest. That is $15 in interest. So, the remaining $35 is deducted from your debt, which leaves you with a debt of $ The next month, you pay interest of 1.5% of $965.00, which is $ Hence, you can deduct $35.52 (which is $50 $14.48) from the amount you owe.

43 Exercise 21 Write a program that tells you how many months it will take you to pay off the loan, as well as the total amount of interest paid over the life of the loan. Use a loop to calculate the amount of interest and the size of the debt after each month. Use a variable to count the number of loop iterations and hence, the number of months until the debt is zero. You may want to use other variables as well. The last payment may be less than $50 if the debt is small, but do not forget the interest. If you owe $50, your monthly payment of $50 will not pay off your debt, although it will come close. One month s interest on $50 is only 75 cents.

44 Exercise 21 Solution

45 Exercise 21 Solution