4.9. Multiple Choice Exercises¶

4.9.1. Easier Multiple Choice Questions¶

4-9-1: What does the following code print?

for (int i = 3; i <= 12; i++)
{
   System.out.print(i + " ");
}

5 6 7 8 9
What is i set to in the initialization area?
4 5 6 7 8 9 10 11 12
What is i set to in the initialization area?
3 5 7 9 11
This loop changes i by 1 each time in the change area.
3 4 5 6 7 8 9 10 11 12
The value of i starts at 3 and this loop will execute until i equals 12. The last time through the loop the value of i is 12 at the begininng and then it will be incremented to 13 which stops the loop since 13 is not less than or equal to 12.

4-9-2: How many times does the following method print a *?

for (int i = 3; i < 9; i++)
{
   System.out.print("*");
}

9
This would be true if i started at 0.
7
Note that it stops when i is 9.
6
Since i starts at 3 and the last time through the loop it is 8 the loop executes 8 - 3 + 1 times = 6 times.
10
This would be true if i started at 0 and ended when i was 10. Does it?

4-9-3: What does the following code print?

int x = -5;
while (x < 0)
{
   x++;
   System.out.print(x + " ");
}

5 4 3 2 1
x is initialized (set) to -5 to start.
-5 -4 -3 -2 -1
x is incremented (x++) before the print statement executes.
-4 -3 -2 -1 0
x is set to -5 to start but then incremented by 1 so it first prints -4.

4-9-4: How many times does the following method print a *?

for (int i = 5; i <= 12; i++)
{
   System.out.print("*");
}

7
This would be true if it stopped when i was 12, but it loops when i is 12.
8
Note that it stops when i is 13 so 13 - 5 is 8.
12
This would be true if i started at 1.
13
This would be true if i started at 0.

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4-9-5: How many times does the following method print a *?

for (int i = 1; i < 5; i++)
{
   System.out.print("*");
}

4
The loop starts with i = 1 and loops as long as it is less than 5 so i is 1, 2, 3, 4.
5
This would be true if the condition was i <= 5.
6
This would be true if i started at 0 and ended when it reached 6 (i <= 5).

4-9-6: How many times does the following method print a *?

for (int i = 0; i <= 8; i++)
{
   System.out.print("*");
}

7
This would be true if i started at 1 and ended when it reached 8.
8
This would be true if the loop ended when i reached 8.
9
This loop starts with i = 0 and continues till it reaches 9 so (9 - 0 = 9).

4-9-7: How many times does the following method print a *?

for (int x = 0; x < 5; x++)
{
   System.out.print("*");
}

4
This would be true if x started at 1 instead of 0.
5
The loop starts with x = 0 and ends when it reaches 5 so 5 - 0 = 5.
6
This would be true if the condition was x <= 5 instead of x = 5.

4-9-8: How many times does the following method print a *?

for (int x = 2; x < 8; x++)
{
   System.out.print("*");
}

6
This loop starts with x = 2 and continues while it is less than 8 so 8 - 2 = 6.
7
This would be true if the loop ended when x was 9 instead of 8 (x <= 8).
8
This would be true if the loop started with x = 0.

4-9-9: What does the following code print?

int x = 0;
while (x <= 5)
{
   System.out.print(x + " ");
   x++;
}

1 2 3 4
This would be true if x started at 1 and ended when x was 5.
1 2 3 4 5
This would be true if x started at 1.
0 1 2 3 4
This would be true if the loop ended when x was 5.
0 1 2 3 4 5
This loop starts with x = 0 and ends when it reaches 6.

4-9-10: What does the following code print?

int x = 3;
while (x < 9)
{
   System.out.print(x + " ");
}

3 4 5 6 7 8
Notice that x isn't changed in the loop.
3 4 5 6 7 8 9
Notice that x isn't changed in the loop.
0 1 2 3 4 5 6 7 8
Notice that x isn't changed in the loop.
0 1 2 3 4 5 6 7 8 9
Notice that x isn't changed in the loop.
It is an infinite loop
Since x is never changed in the loop this is an infinite loop.

4.9.2. Medium Multiple Choice Questions¶

4-9-11: How many stars are output when the following code is executed?

for (int i = 0; i < 5; i++) {
   for (int j = 0; j < 5; j++)
      System.out.println("*");
}

10
The second loop executes 5 times for each of the 5 times the first loop executes, so the answer should be 5 * 5.
5
The second loop executes 5 times for each of the 5 times the first loop executes, so the answer should be 5 * 5.
25
The first loop will execute 5 times, and for each time through, the second loop will execute 5 times. So the answer is the number of times through the first loop times the number of times through the second.
50
The second loop executes 5 times for each of the 5 times the first loop executes, so the answer should be 5 * 5.
15
The second loop executes 5 times for each of the 5 times the first loop executes, so the answer should be 5 * 5.

4-9-12: Which of the following code segments will produce the displayed output?

1
22
333
4444
55555


I.   for (int i = 1; i <= 5; i++) {
        for (int j = i; j > 0; j--) {
           System.out.print(i);
        }
        System.out.println();
     }

II.  for (int i = 0; i < 5; i++) {
        for (int j = 0; j < i; j++) {
           System.out.print(i);
        }
        System.out.println();
     }

III. for (int i = 1; i < 5; i++) {
        for (int j = i; j > 0; j--) {
           System.out.print(i);
        }
        System.out.println();
     }

IV.  for (int i = 1; i < 6; i++) {
        for (int j = 0; j < i; j++) {
           System.out.println(i);
        }
     }

V.   for (int i = 0; i < 5; i++) {
        for (int j = 0; j < i; j++) {
           System.out.print(i+1);
        }
        System.out.println();
     }

I
This will loop with i changing from 1 to 5 and then for each i, j will loop from i to 0 printing the value of i and then a new line.
II
This will loop i from 0 to 4 and j from 0 to i, neglecting to ouput 5.
III
This will loop with i changing from 1 to 4 and j from i to 0.
IV
This will loop with i changing from 1 to 5 and j from 0 to i but it will print each value on a different line.
V
This will loop with i changing from 0 to 4 and j from 0 to i.

4-9-13: What is printed as a result of the following code segment?

for (int k = 0; k < 20; k+=2) {
   if (k % 3 == 1)
      System.out.print(k + " ");
}

0 2 4 6 8 10 12 14 16 18
This would be correct if we were printing out all of the values of k, not just the ones that have a remainder of 1 when divided by 3.
4 16
This is missing the value 10 (10 divided by 3 does have a remainder of 1).
0 6 12 18
None of these answers have a remainder of 1 when divided by 3.
1 4 7 10 13 16 19
This answer would be correct if k was incremented by 1 instead of 2. K will be 0, 2, 4, 6, 8, 10, 12, 14, 16, 18 in this loop.
4 10 16
This will loop with k having a value of 0 to 18 (it will stop when k = 20). It will print out the value of k followed by a space when the remainder of dividing k by 3 is 1.

4-9-14: Which of the following code segments will produce the displayed output?

11111
2222
333
44
5


I.   for (int j = 1; j <= 5; j++) {
        for (int k = 5; k >= j; k--) {
           System.out.print(j + " ");
        }
        System.out.println();
     }

II.  for (int j = 1; j <= 5; j++) {
        for (int k = 5; k >= 1; k--) {
           System.out.print(j + " ");
        }
        System.out.println();
     }

III. for (int j = 1; j <= 5; j++) {
        for (int k = 1; k <= j; k++) {
           System.out.print(j + " ");
        }
        System.out.println();
     }

IV.  for (int j = 1; j <= 5; j++) {
        for (int k = 1; k <= 5; k++) {
           System.out.println(j + " ");
        }
     }

V.   for (int j = 1; j <= 5; j++) {
        for (int k = j; k <= 5; k++) {
           System.out.print(k + " ");
        }
        System.out.println();
     }

I
This will loop with j from 1 to 5 and k from 5 to j and print out the value of j and a space. So the first time through the loop it will print 1 five times and the next time it will print out 2 four times and so on.
II
This will print out each value from 1 to 5 five times.
III
This will loop with j from 1 to 5 and k from 1 times.
IV
This will loop j from 1 to 5 and k from 1 to 5, printing each number 5 times.
V
This loops with j from 1 to 5 and k from j to 5 and prints out the value of k, printing 1 through 5 on the first line, 2 through 5 on the next, and so on.

4-9-15: What are the values of var1 and var2 after the following code segment is executed and the while loop finishes?

int var1 = 0;
int var2 = 2;

while ((var2 != 0) && ((var1 / var2) >= 0)) {
   var1 = var1 + 1;
   var2 = var2 - 1;
}

var1 = 0, var2 = 2
This would be true if the body of the while loop never executed. This would have happened if the while check was if var1 != 0 instead of var2 != 0
var1 = 1, var2 = 1
This would be true if the body of the while loop only execued one time, but it executes twice.
var1 = 3, var2 = -1
This would be true if the body of the while loop executed 3 times, but it executes twice.
var1 = 2, var2 = 0
The loop starts with var1=0 and var2=2. The while checks that var2 isn't 0 and that var1/var2 is greater than or equal to zero (0/2=0) so this is equal to zero and the body of the while loop will execute. The variable var1 has 1 added to it for a new value of 1. The variable var2 has 1 subtracted from it for a value of 1. At this point var1=1 and var2=1. The while condition is checked again. Since var2 isn't 0 and var1/var2 (1/1=1) is >=0 so the body of the loop will execute a second time. The variable var1 has 1 added to it for a new value of 2. The variable var2 has 1 subtracted from it for a value of 0. At this point var1=2 and var2=0. The while condition is checked again. Since var2 is zero the while loop stops and the value of var1 is 2 and var2 is 0.
The loop won't finish executing because of a division by zero.
0/2 won't cause a division by zero. The result is just zero.

4.9.3. More Practice¶

For more practice with loops and strings see http://codingbat.com/java/Warmup-2. For practice with loops and arrays see http://codingbat.com/java/Array-2.

Here are some recommended problems