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CSE142 Sample Midterm, Autumn 2017
1. Expressions, 10 points. For each expression in the left-hand column,
indicate its value in the right-hand column. Be sure to list a constant of
appropriate type (e.g., 7.0 rather than 7 for a double, Strings in quotes).
Expression Value
5 * 6 - (4 + 3) * 2 - 2 * 3 ________________
208 / 20 / 4 + 12 / 10.0 + 0.4 * 2 ________________
8 - 2 + "8 - 2" + 8 * 2 + 8 ________________
4 * 5 % 6 + 297 % 10 + 4 % 8 ________________
13 / 2 * 3.0 + 5.5 * 3 / 2 ________________
2. Parameter Mystery, 12 points. Consider the following program.
public class Mystery {
public static void main(String[] args) {
String x = "chair";
String y = "notes";
String z = "table";
String meeting = "x";
String notes = y + meeting;
meeting(x, y, z);
meeting(y, meeting, "notes");
meeting(y + z, y + meeting, notes);
meeting = "boring";
meeting(meeting, "today", x);
}
public static void meeting(String z, String y, String x) {
System.out.println(x + " and " + z + " like " + y);
}
}
List below the output produced by this program.
3. If/Else Simulation, 12 points. Consider the following method.
public static void ifElseMystery(int a, int b) {
if (a < b && b % 2 == 1) {
a = a + 4;
} else if (a % 2 == 0) {
a++;
}
if (a < b || a % 2 == 0) {
a = a + 2;
b--;
} else {
a = a - 2;
b = b + 10;
}
System.out.println(a + " " + b);
}
For each call below, indicate what output is produced.
Method Call Output Produced
ifElseMystery(6, 5); _______________
ifElseMystery(4, 6); _______________
ifElseMystery(9, 5); _______________
ifElseMystery(3, 6); _______________
ifElseMystery(2, 7); _______________
ifElseMystery(1, 3); _______________
4. While Loop Simulation, 12 points. Consider the following method:
public static void mystery(int n) {
int x = 0;
int y = 0;
while (n > 0 && n % 2 == 0) {
x++;
y = y * 10 + n % 10;
n = n / 10;
}
System.out.println(x + " " + y);
}
For each call below, indicate what output is produced.
Method Call Output Produced
mystery(5); _______________
mystery(8); _______________
mystery(346); _______________
mystery(265408); _______________
5. Assertions, 15 points. You will identify various assertions as being either
always true, never true or sometimes true/sometimes false at various points
in program execution. The comments in the method below indicate the points
of interest.
public static void mystery(Scanner console) {
int x = 3;
int y = 0;
// Point A
while (x > 0) {
// Point B
x = console.nextInt();
y++;
if (x > 0) {
x = -x;
// Point C
}
// Point D
x = -x;
}
// Point E
System.out.println("y = " + y);
}
Fill in the table below with the words ALWAYS, NEVER or SOMETIMES.
x > 0 x == 0 y == 0
+---------------------+---------------------+---------------------+
Point A | | | |
+---------------------+---------------------+---------------------+
Point B | | | |
+---------------------+---------------------+---------------------+
Point C | | | |
+---------------------+---------------------+---------------------+
Point D | | | |
+---------------------+---------------------+---------------------+
Point E | | | |
+---------------------+---------------------+---------------------+
6. Programming, 15 points. Write a static method called printSum that takes an
integer n and integers low and high as parameters and that produces a series
of n integers between low and high inclusive, printing various information
about the integers. The method should construct and use a Random object to
generate the numbers. For example, if you make the following call:
printSum(15, 4, 8);
the method should produce three lines of output like the following:
sum 15 numbers 4 to 8
6 + 6 + 4 + 6 + 6 + 8 + 8 + 7 + 8 + 4 + 8 + 7 + 6 + 6 + 8 = 98
max = 98
The first line indicates that the method is going to find the sum of 15
numbers between 4 and 8 inclusive (as indicated by the parameters in the
call). The second line shows the 15 numbers randomly selected by the method
and their sum. The third line reports the highest partial sum for the
series. A partial sum is obtained by adding up a limited number of terms
starting with the first term (in the example above, a sum of 6 for the first
term, a sum of 12 for the first two terms, a sum of 16 for the first three
terms, and so on). In this case, the maximum sum is the overall sum, but
that won't always be the case. For example, if the call instead had been:
printSum(10, -2, 2);
the output would look like the following:
sum 10 numbers -2 to 2
-1 + 2 + 2 + 2 + -1 + -1 + -2 + 2 + 0 + -1 = 2
max = 5
Here the maximum sum occurs with the first four numbers that add up to 5.
You are to exactly reproduce the format of these logs. You may assume that
n is greater than or equal to 1 and that low is less than or equal to high.
7. Programming, 15 points. Write a static method called tallyVotes that takes
a console Scanner as a parameter and that prompts the user for a series of
votes, reporting and returning the percentage of yes votes. The user is
prompted for a series of responses that are either "y" to indicate yes, "n"
to indicate no, or "q" to indicate that the user wants to quit because there
are no more votes to tally. You can assume that the user will always type
one of these three responses as a lowercase letter. For example, below is a
sample call on the method:
Scanner console = new Scanner(System.in);
double percentYes = tallyVotes(console);
This call would produce an interaction like the following (with the user
typing "y", "n", or "q"):
vote? y
vote? y
vote? n
vote? y
vote? y
vote? y
vote? q
total votes = 6
result = 83.33333333333334%
Notice that the user is prompted for votes until they quit and then the
method produces a line of output showing the total number of votes and a
line of output showing the percent of yes votes. You do not need to round
the percentage. The variable percentYes would be set to 83.33333333333334.
You are to exactly reproduce the format of this log. You may assume that
the user enters at least one vote before quitting.
8. Programming, 9 points. Write a static method called undouble that takes a
string as a parameter and that returns a new string obtained by replacing
every pair of repeated adjacent letters with one of that letter. For
example, the String "bookkeeper" has three repeated adjacent letters ("oo",
"kk", and "ee"), so undouble("bookkeeper") should return the string
"bokeper". Below are more sample calls:
Method Value Method Value
Call Returned Call Returned
--------------------------------- ---------------------------------
undouble("odegaard") "odegard" undouble("oops") "ops"
undouble("baz") "baz" undouble("foobar") "fobar"
undouble("mississippi") "misisipi" undouble("apple") "aple"
undouble("carry") "cary" undouble("berry") "bery"
undouble("juggle") "jugle" undouble("theses") "theses"
undouble("little") "litle" undouble("") ""
You may assume that the string is composed entirely of lowercase letters, as
in the examples above, and that no letter appears more than two times in a
row. But notice that the method might be passed an empty string, in which
case it returns an empty string. You may use only the string methods
included on the cheat sheet. In particular, you may not use the replace
method of the String class to solve this problem.
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