Sample Prelim 1 Questions (FROM CS100A, Fall 1999)

Notes:

__ Read ALL directions. In particular, when we give you a checklist, make sure you observe each requirement!

__ This is not a sample prelim: It is too long.

1. (Short Answer) Each line in the program segment below has something wrong with it. Fix each line.

int 3 = x;
if (7 - x = 4)
System.Out.Println("four is " + 4);
int x = "4";
if (3 < 4, 4 < 5)
System.out.println(4 is between 3 and 5);

2. (Short Answer) Briefly answer each question below.

(a) What is the difference between "=" and "=="?

(b) What is the difference among the following three statements?

i) int x; ii) int x = 3; iii) x = 3;

(c) Is there any difference between "fred" and "Fred"?

(d) Assume the code below is correct. Indent it properly. Note that there is more than one correct answer.

while (x<0) { counter *= 10; if (y<z) y++; else z = z*2; x = x+2; w = w/7; }

3. (Tracing) Trace the code segment below -- fill in the table below using the format of one column per assignment, one entry per column. The first three assignments have already been done for you.

int n = 19, x = 0, y = 1;
while (n != 0)
if (n % 2 == 0)
n = n/2;
else {
n = n-1;
x = 10*x + 3;
y = y*10;
}
y = (y-1) / 3;

+----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
n | 19 | | | | | | | | | | | | | | | | | |
+----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
x | | 0 | | | | | | | | | | | | | | | | |
+----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+
y | | | 1 | | | | | | | | | | | | | | | |
+----+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+---+

4. (Iteration) Write a program segment to read a positive integer n from input and print a hollow n-triangle. Examples for 1, 2, 3, 4, 5 are shown below.

__ Assume TokenReader in = new TokenReader(System.in); has already been included.

__ Use good style

__ Clearly indicate in a comment how many "hollow" spaces you intend to print on each line.

__ Do NOT use Format.print.

*
* **
* ** * *
* ** * * * *
* ** *** **** *****

5. (Iteration) Same as question 4, but orient the triangles as shown below, and include the additional requirement below.

__ Clearly indicate in a comment how many "padding" spaces you intend to on each line before the first star.

* ** *** **** *****
* ** * * * *
* ** * *
* **
*

6. (Processing Input) The Cornell psychology department is known in part for its sleep lab. Write a program to help them out.

Write the program

__ using good style,

__ to read in a log of sleep sessions during one month,

__ and at the end of the month, print how many days the person
is asleep in 3 or more separate sessions during that day.

The input format is a sequence of integers in groups of 2 representing sleep sessions in chronological order.

__ The first integer is the day the sleep session starts.

__ The second integer is the length of the session in minutes.

__ The sequence is terminated by 0 0.

__ For simplicity, the person is always still awake at midnight, so that no sleep session starts on one day and ends on another day.