Show the output of the following programs. (Hint: Draw a table and list the variables in the columns to trace these programs.)

a.

Public class Test {
  Public static void main (String[] args) {
    for (int i = 1; i < 5; i++) {
      int j = 0;
      while (j < i) {
        System.out.print(j + " ");
        j++;
      }
     }
   }
 }

b.

Public class Test {
  Public static void main (String[] args) {
      int i = 0;
      while (i < 5) {
       for (int j = i; j < 1; j--)
        System.out.print(j + " ");
       System.out.println("****");
        i++;
      }
     }
   }

c.

Public class Test {
  Public static void main(String[] args) {
    int i = 5;
    while (i >= 1) {
      int num = 1;
      for(int j = 1; j <= i; j++) {
        System.out.print(num + "xxx");
        num *= 2;
      }
      System.out.println();
      i--;
    }
  }
}

d.

Public class Test {
  Public static void main(String[] args) {
    int i = 1;
    do {
      int num = 1;
      for(int j = 1; j <= i; j++) {
        System.out.print(num + "C");
        num *= 2;
      }
      System.out.println();
      i++;
    } while (i <= 5);
  }
}

The program given below generates five random subtraction questions. Revise the program to generate ten random addition questions for two integers between 1 and 15. Display the correct count and test time.

1   import java.util.Scanner;
2
3   public class SubtractionQuizLoop {
4       public static void main(String[] args) {
5           final int NUMBER_OF_QUESTIONS = 5; // Number of questions
6           int correctCount = 0; // Count the number of correct answers
7           int count = 0; // Count the number of questions
8           long startTime = System.currentTimeMillis();
9           String output = " "; // output string is initially empty
10          Scanner input = new Scanner(System.in);
11
12          while (count < NUMBER_OF_QUESTIONS) {
13              // 1. Generate two random single-digit integers
14              int number1 = (int)(Math.random() * 10);
15              int number2 = (int)(Math.random() * 10);
16
17              // 2. If number1 < number2, swap number1 with number2
18              if (number1 < number2) {
19                  int temp = number1;
20                  number1 = number2;
21                  number2 = temp;
22              }
23
24              // 3. Prompt the student to answer "What is number1 – number2?"
25              System.out.print(
26              "What is " + number1 + " - " + number2 + "? ");
27              int answer = input.nextInt();
28
29              // 4. Grade the answer and display the result
30              if (number1 - number2 == answer) {
31                  System.out.println("You are correct!");
32                  correctCount++; // Increase the correct answer count
33              }
34              else
35                  System.out.println("Your answer is wrong.\n" + number1
36                  + " - " + number2 + " should be " + (number1 - number2));
37
38              // Increase the question count
39              count++;
40
41              output += "\n" + number1 + "-" + number2 + "=" + answer +
42              ((number1 - number2 == answer) ? " correct" : " wrong");
43          }
44
45          long endTime = System.currentTimeMillis();
46          long testTime = endTime - startTime;
47
48          System.out.println("Correct count is " + correctCount +
49          "\nTest time is " + testTime / 1000 + " seconds\n" + output);
50      }
51  }

Write a nested for loop that prints the following output:

                  1
              1   2  1
            1 2   4  2  1
        1   2 4   8  4  2  1
      1 2   4 8  16  8  4  2  1
    1 2 4   8 16 32  16 8  4  2 1
  1 2 4 8  16 32 64  32 16 8  4 2 1
1 2 4 8 16 32 64 128 64 32 16 8 4 2 1

Suppose the input is 2 3 4 5 0. What is the output of the following code?

import java.util.Scanner;
public class Test {
 public static void main(String[] args) {
 Scanner input = new Scanner(System.in);
 int number, sum = 0, count;
 for (count = 0; count < 5; count++) {
 number = input.nextInt();
 sum += number;
 }
 System.out.println("sum is " + sum);
 System.out.println("count is " + count);
 }
}

Can you always convert a while loop into a for loop? Convert the following while loop into a for loop:

int i = 1;
int sum = 0;
while (sum < 10000) {
 sum = sum + i;
 i++;
}

Will the program work if n1 and n2 are replaced by n1 / 2 and n2 / 2 in line 17 in Listing 5.9?

What is wrong if guess is initialized to 0 in line 11 in Listing 5.3?

(Find the factors of an integer) Write a program that reads an integer and displays all its smallest factors in an increasing order. For example, if the input integer is 120, the output should be as follows: 2, 2, 2, 3, 5.

Use nested loops that display the following patterns in four separate programs:

Pattern A       Pattern B        Pattern C       Pattern D
1               1 2 3 4 5 6               1     1 2 3 4 5 6
1 2             1 2 3 4 5               2 1     1 2 3 4 5
1 2 3           1 2 3 4               3 2 1     1 2 3 4
1 2 3 4         1 2 3               4 3 2 1     1 2 3
1 2 3 4 5       1 2               5 4 3 2 1     1 2
1 2 3 4 5 6     1               6 5 4 3 2 1     1

Write a program that prompts the user to enter an integer from 1 to 15 and displays a pyramid, as shown in the following sample run:

Enter the number of lines: 7 <enter>
                                    1
                                  2 1 2
                                3 2 1 2 3
                              4 3 2 1 2 3 4
                            5 4 3 2 1 2 3 4 5
                          6 5 4 3 2 1 2 3 4 5 6
                        7 6 5 4 3 2 1 2 3 4 5 6 7

(Display the ASCII character table) Write a program that prints the characters in the ASCII character table from ! to ~. Display 10 characters per line. The ASCII table is given in Appendix B. Characters are separated by exactly one space.

Declare a char variable grade and set the value of grade to 'A'.

(Compute the greatest common divisor) Another solution for Listing 5.9 to find the greatest common divisor of two integers n1 and n2 is as follows: First find d to be the minimum of n1 and n2, then check whether d, d–1, d–2, , 2, or 1 is a divisor for both n1 and n2 in this order. The first such common divisor is the greatest common divisor for n1 and n2. Write a program that prompts the user to enter two positive integers and displays the gcd

Can you convert a for loop to a while loop? List the advantages of using for loops.