1. Peer Instruction 4
Control Loops

2. cs163/164: Peer 4 - Control Loops - Fall Semester 2016
What value is printed for the loop variable when the code shown below runs?
int loop = 0; while (loop <= 11) { loop++; System.out.println(loop); }
0 to 9
0 to 10
1 to 10
1 to 11
None of the above
Correct answer is D, loop executes with i = 0..10, but print is after increment so
Bonus: What if the post increment is inside print! Answer: The code prints instead of
While Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

3. cs163/164: Peer 4 - Control Loops - Fall Semester 2016
What value is printed for the loop variable when the code shown below runs?
int loop = 0; while (loop <= 11) { loop++; System.out.println(loop); }
0 to 9
0 to 10
1 to 10
1 to 11
None of the above
Correct answer is D, loop executes with i = 0..10, but print is after increment so
Bonus: What if the post increment is inside print! Answer: The code prints instead of
While Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

4. cs163/164: Peer 4 - Control Loops - Fall Semester 2016
What value is printed for the loop variable when the code shown below runs?
int loop =0; while (0 <= loop <= 8) { loop++; } System.out.println(loop); 9 10 11 12
Will not compile!
Correct answer is C, condition fails when i is 11, so loop body is not executed, but i is incremented.
Bonus: How many times is condition evaluated? Answer: 11 times, 10 times true and 1 time false!
While Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

5. cs163/164: Peer 4 - Control Loops - Fall Semester 2016
What value is printed for the loop variable when the code shown below runs?
int loop =0; while (0 <= loop <= 8) { loop++; } System.out.println(loop); 9 10 11 12
Will not compile!
Correct answer is C, condition fails when i is 11, so loop body is not executed, but i is incremented.
Bonus: How many times is condition evaluated? Answer: 11 times, 10 times true and 1 time false!
While Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

6. How many times will the body of the ‘do while’ loop execute?
byte loop = -5; do { loop++; } while (loop > 0);
0 times
1 time
2 times
128 times
Infinite loop!
Correct answer is B, only one time, do while always executes at least once.
Do While Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

7. How many times will the body of the ‘do while’ loop execute?
byte loop = -5; do { loop++; } while (loop > 0);
0 times
1 time
2 times
128 times
Infinite loop!
Correct answer is B, only one time, do while always executes at least once.
Do While Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

8. cs163/164: Peer 4 - Control Loops - Fall Semester 2016
What is printed below?
for (int i = 0; i<10; ++i) {
System.out.println(i); }
0 to 9
0 to 10
1 to 9
1 to 10
None of the above
Correct answer is C, adds exclamation points one at a time until string length is 10.
String Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

9. cs163/164: Peer 4 - Control Loops - Fall Semester 2016
What is printed below?
for (int i = 0; i<10; ++i) {
System.out.println(i); }
0 to 9
0 to 10
1 to 9
1 to 10
None of the above
Correct answer is C, adds exclamation points one at a time until string length is 10.
String Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

10. How many lines does the nested loop shown below print?
for (int row = 0; row < 10; row += 2) {
for (int col = 0; col < 50; col += 10) {
System.out.println(row + "," + col) { }
20 times
25 times
36 times
500 times
Different each time it runs!
Nested Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

11. How many lines does the nested loop shown below print?
for (int row = 0; row < 10; row += 2) {
for (int col = 0; col < 50; col += 10) {
System.out.println(row + "," + col) { }
20 times
25 times
36 times
500 times
Different each time it runs!
Nested Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

12. cs163/164: Peer 4 - Control Loops - Fall Semester 2016
Which of the following correctly prints the entire contents of the string?
String s = "Programming is fun!";
for (int i=1; i< s.length(); i++) { System.out.print(s.charAt(i)); }
for (int i=1; i<= s.length(); ++i) { System.out.print(s.charAt(i)); }
for (int i=0; i<= s.length(); i++) { System.out.print(s.charAt(i)); }
for (int i=0; i< s.length(); ++i) { System.out.print(s.charAt(i)); }
None of the above
Correct answer is D, must start at zero and end at length – 1.
String Enumeration
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

13. cs163/164: Peer 4 - Control Loops - Fall Semester 2016
Which of the following correctly prints the entire contents of the string?
String s = "Programming is fun!";
for (int i=1; i< s.length(); i++) { System.out.print(s.charAt(i)); }
for (int i=1; i<= s.length(); ++i) { System.out.print(s.charAt(i)); }
for (int i=0; i<= s.length(); i++) { System.out.print(s.charAt(i)); }
for (int i=0; i< s.length(); ++i) { System.out.print(s.charAt(i)); }
None of the above
Correct answer is D, must start at zero and end at length – 1.
String Enumeration
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

14. What is the last line printed by the ‘for’ loop shown below?
for (String s = "Hello"; s.length() <= 10; s += "!") {
System.out.println(s); }
Hello
Hello!
Hello!!!!!
!!!!!
None of the above
Correct answer is C, adds exclamation points one at a time until string length is 10.
String Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

15. What is the last line printed by the ‘for’ loop shown below?
for (String s = "Hello"; s.length() <= 10; s += "!") {
System.out.println(s); }
Hello
Hello!
Hello!!!!!
!!!!!
None of the above
Correct answer is C, adds exclamation points one at a time until string length is 10.
String Loops
cs163/164: Peer 4 - Control Loops - Fall Semester 2016

16. Methods and Parameters
Peer Instruction 5
Methods and Parameters

17. cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016
Which statement is a valid invocation of a method with and int and float parameter?
myMethod(int i = 12, float f = 2.3);
myMethod((int) 12, (float) 2.3f);
myMethod(int i, float f);
myMethod(int, float);
myMethod(12.0, 2.3f);
cannot specify data type, cannot have initializer
is correct, but type casts are redundant
cannot specify data type, compiler already knows
is ridiculous, not actual parameters, just data types
first parameter cannot be double, second is okay
NOTE: actual parameters are those used to invoke method, also called arguments
Actual Paramaters
cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016

18. cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016
Which statement is a valid invocation of a method with and int and float parameter?
myMethod(int i = 12, float f = 2.3);
myMethod((int) 12, (float) 2.3f);
myMethod(int i, float f);
myMethod(int, float);
myMethod(12.0, 2.3f);
cannot specify data type, cannot have initializer
is correct, but type casts are redundant
cannot specify data type, compiler already knows
is ridiculous, not actual parameters, just data types
first parameter cannot be double, second is okay
NOTE: actual parameters are those used to invoke method, also called arguments
Actual Paramaters
cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016

19. cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016
Which line of code uses the integer return value from the method correctly?
System.out.println(calculateInteger());
int myInteger = calculateInteger();
double myDouble = (5.0 * calculateInteger()) / ;
double myDouble = Math.max(calculateInteger(), 1234);
All of the above
Answer is E), anywhere a literal or variable of type int can be used you can have an int return value.
Return Values
cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016

20. cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016
Which line of code uses the integer return value from the method correctly?
System.out.println(calculateInteger());
int myInteger = calculateInteger();
double myDouble = (5.0 * calculateInteger()) / ;
double myDouble = Math.max(calculateInteger(), 1234);
All of the above
Answer is E), anywhere a literal or variable of type int can be used you can have an int return value.
Return Values
cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016

21. What are the limitations of single return value from a method?
A single primitive (byte, int, float, double, char, boolean, ...)
A single primitive or an array of primitives
A single class, (String, Scanner, ...)
A single class or an array of classes
All of the above
Answer is E), thus it’s not much of a limitation!
Return Values
cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016

22. What are the limitations of single return value from a method?
A single primitive (byte, int, float, double, char, boolean, ...)
A single primitive or an array of primitives
A single class, (String, Scanner, ...)
A single class or an array of classes
All of the above
Answer is E), thus it’s not much of a limitation!
Return Values
cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016

23. cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016
Given the code below, what is output by the two print statements, in order of execution?
// Code fragment
int value = 6;
printSquare(value);
System.out.println(value);
public static void printSquare(int value) {
value = value * value; }
6, 6
36, 6
36, 36
6, 36
None of the above
Answer is B), value variables are completely difference memory locations, parameter is squared but not returned
NOTE: Naming the actual and formal parameters the same is misleading!
Pass by Value
cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016

24. cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016
Given the code below, what is output by the two print statements, in order of execution?
// Code fragment
int value = 6;
printSquare(value);
System.out.println(value);
public static void printSquare(int value) {
value = value * value; }
6, 6
36, 6
36, 36
6, 36
None of the above
Answer is B), value variables are completely difference memory locations, parameter is squared but not returned
NOTE: Naming the actual and formal parameters the same is misleading!
Pass by Value
cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016

25. cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016
How many activation records are on the stack when executing code in Math.sin?
// code fragment in main
foo(1.0);
public static void foo(double d) {
d += bar(d * d) ; }
public static void bar(double d) {
d *= Math.sin(Math.PI); 1 2 3 4
E) is correct: main, myMethod0, myMethod1, Math.sin
What if bar called foo? What of bar called bar?
Pass by Value
cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016

26. cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016
How many activation records are on the stack when executing code in Math.sin?
// code fragment in main
foo(1.0);
public static void foo(double d) {
d += bar(d * d) ; }
public static void bar(double d) {
d *= Math.sin(Math.PI); 1 2 3 4
E) is correct: main, myMethod0, myMethod1, Math.sin
What if bar called foo? What of bar called bar?
Pass by Value
cs163/164: Peer 5 - Methods and Parameters - Fall Semester 2016

27. Peer Instruction 6
Java Arrays

28. cs163/164: Peer 6 - Java Arrays - Fall Semester 2016
Which of the following correctly declares, allocates, and initializes an array?
int iArray[5] = {1, 2, 3, 4, 5};
short sArray[4] = new short[4];
char cArray = {‘a’, ‘b’, ‘c’, ‘d’};
double dArray[] = new double {11.1, 22.2, 33.3};
String sArray[] = {"Java ", "Fortran", "C++"};
A) will not compile, cannot specify size
B) will not compile, cannot specify size
C) will not compile, variable is not an array
D) will not compile, add square brackets or remove ‘new double’
E) is correct, long form of initialization, new String[] can be omitted
Array Declaration
cs163/164: Peer 6 - Java Arrays - Fall Semester 2016

29. cs163/164: Peer 6 - Java Arrays - Fall Semester 2016
Which of the following correctly declares, allocates, and initializes an array?
int iArray[5] = {1, 2, 3, 4, 5};
short sArray[4] = new short[4];
char cArray = {‘a’, ‘b’, ‘c’, ‘d’};
double dArray[] = new double {11.1, 22.2, 33.3};
String sArray[] = {"Java ", "Fortran", "C++"};
A) will not compile, cannot specify size
B) will not compile, cannot specify size
C) will not compile, variable is not an array
D) will not compile, add square brackets or remove ‘new double’
E) is correct, long form of initialization, new String[] can be omitted
Array Declaration
cs163/164: Peer 6 - Java Arrays - Fall Semester 2016

30. cs163/164: Peer 6 - Java Arrays - Fall Semester 2016
Which of the following correctly prints out the fourth element of iArray?
System.out.println(iArray + 4);
System.out.println(iArray[4]);
System.out.println([4]iArray);
System.out.println(iArray(4));
None of the above
is ridiculous, cannot add array and integer
accesses the fifth element, otherwise okay
actually works in ‘C’ language, not java, wrong index again
cannot use parentheses instead of brackets, wrong index again
E) is correct
Array Access
cs163/164: Peer 6 - Java Arrays - Fall Semester 2016

31. cs163/164: Peer 6 - Java Arrays - Fall Semester 2016
Which of the following correctly prints out the fourth element of iArray?
System.out.println(iArray + 4);
System.out.println(iArray[4]);
System.out.println([4]iArray);
System.out.println(iArray(4));
None of the above
is ridiculous, cannot add array and integer
accesses the fifth element, otherwise okay
actually works in ‘C’ language, not java, wrong index again
cannot use parentheses instead of brackets, wrong index again
E) is correct
Array Access
cs163/164: Peer 6 - Java Arrays - Fall Semester 2016

32. cs163/164: Peer 6 - Java Arrays - Fall Semester 2016
Which of the following correctly increments all the elements of iArray?
for (int i=0; i < iArray.length(); i++) iArray[i]++;
for (int i=1; i <= iArray.length; i++) iArray[i]++;
for (int i=0; i < iArray.length;) iArray[i++]++;
iArray[0..iArray.length]++;
iArray++;
has extra parentheses
loop index starts at second element
is correct
would be nice, but Java doesn’t have .. range operator
is ridiculous
Array Loops
cs163/164: Peer 6 - Java Arrays - Fall Semester 2016

33. cs163/164: Peer 6 - Java Arrays - Fall Semester 2016
Which of the following correctly increments all the elements of iArray?
for (int i=0; i < iArray.length(); i++) iArray[i]++;
for (int i=1; i <= iArray.length; i++) iArray[i]++;
for (int i=0; i < iArray.length;) iArray[i++]++;
iArray[0..iArray.length]++;
iArray++;
has extra parentheses
loop index starts at second element
is correct
would be nice, but Java doesn’t have .. range operator
is ridiculous
Array Loops
cs163/164: Peer 6 - Java Arrays - Fall Semester 2016

34. Two-Dimensional Arrays
Peer Instruction 7
Two-Dimensional Arrays

35. Declaration and allocation of two-dimensional (2D) arrays.
Which statements correctly declare and allocate a 2D integer array with 2 rows and 4 columns?
int iArray[2][4];
int iArray = new int[2][4];
int iArray[][] = new int[4][2];
int iArray[][] = new int[2][4];
int iArray[][] = { { 1, 2, 3, 4 }, { 4, 5, 6, 7 } };
2) and 4)
3) and 5)
1) and 5)
4) and 5)
2) and 5)
4) and 5) are correct, 1) does not allocate, 2) is not an array, 3) is backwards, so the answer is E)
2D Array Declaration
cs163/164: Peer 7 - 2D Arrays - Fall Semester 2016

36. Declaration and allocation of two-dimensional (2D) arrays.
Which statements correctly declare and allocate a 2D integer array with 2 rows and 4 columns?
int iArray[2][4];
int iArray = new int[2][4];
int iArray[][] = new int[4][2];
int iArray[][] = new int[2][4];
int iArray[][] = { { 1, 2, 3, 4 }, { 4, 5, 6, 7 } };
2) and 4)
3) and 5)
1) and 5)
4) and 5)
2) and 5)
4) and 5) are correct, 1) does not allocate, 2) is not an array, 3) is backwards, so the answer is E)
2D Array Declaration
cs163/164: Peer 7 - 2D Arrays - Fall Semester 2016

37. Accessing elements in a 2D array (Part 1)
What is the value of cArray[2][1] after the following code has executed?
‘a’
‘b’
‘c’
‘d’
‘e’
char cArray[][] = new char[3][3];
for (int i = 0; i < 3; i++)
for (int j = 0; j < 3; j++)
cArray[i][j] = (char) ('a' + j + i);
The answer is cArray[2][1] = (char) (‘a’ ) = ‘d’, so the answer is D), show the whole array on the board.
2D Array Access
cs163/164: Peer 7 - 2D Arrays - Fall Semester 2016

38. Accessing elements in a 2D array (Part 1)
What is the value of cArray[2][1] after the following code has executed?
‘a’
‘b’
‘c’
‘d’
‘e’
char cArray[][] = new char[3][3];
for (int i = 0; i < 3; i++)
for (int j = 0; j < 3; j++)
cArray[i][j] = (char) ('a' + j + i);
The answer is cArray[2][1] = (char) (‘a’ ) = ‘d’, so the answer is D), show the whole array on the board.
2D Array Access
cs163/164: Peer 7 - 2D Arrays - Fall Semester 2016

39. Accessing elements in a 2D array (Part 2)
Which array element correctly accesses the highlighted value in the array below?
123
234
345
456
567
678
789
890
111
222
333
444
555
666
777
987
876
765
654
543
432
321
210
iArray[4][3]
iArray[3][4]
iArray[3][2]
iArray[2][3]
iArray[3][3]
The answer is C), since row and column are zero-based and Java is row-major.
2D Array Access
cs163/164: Peer 7 - 2D Arrays - Fall Semester 2016

40. Accessing elements in a 2D array (Part 2)
Which array element correctly accesses the highlighted value in the array below?
123
234
345
456
567
678
789
890
111
222
333
444
555
666
777
987
876
765
654
543
432
321
210
iArray[4][3]
iArray[3][4]
iArray[3][2]
iArray[2][3]
iArray[3][3]
The answer is C), since row and column are zero-based and Java is row-major.
2D Array Access
cs163/164: Peer 7 - 2D Arrays - Fall Semester 2016