Description
• Java
while (Test)
{
Body
}
Body
true
false
Test?
Sum of Squares
GIVENS: n (a number ≥ 1)
RESULTS: sum (sum of squares from 12 to n2)
sum ← sum + value * value
value ← value + 1
true
false
sum ← 0
value ← 1
value ≤ n ?
Sum of Odd Integers
GIVENS: n (a number ≥ 1)
RESULTS: sum (sum of odd integers up to n)
sum ← sum + value
value = value + 2
true
false
sum ← 0
value ← 1
value ≤ n ?
Sum of odd integers
What does this program print for n =5. Let’s execute this program on
paper.
Statement n value sum
(User entered 5) Initial values 5 ? ?
Line 7: sum = 0 0
Line 8: value = 1 1
Line 9: value <=n ? (1 <= 5) true
Line 11: sum = sum + value 1
Line 12: value = value + 2 3
Line 9: value <=n ? (3 <= 5) true
Line 11: sum = sum + value 4
Line 12: value = value + 2 5
Line 9: value <=n ? (5 <= 5) true
Line 11: sum = sum + value 9
Line 12: value = value + 2 7
Line 9: value <=n ? (5 <= 5) false
Line 15: System.out.println( …)
Trace for Sum of Odd Integers
Exercise 1 (on paper)
• What does the program
on the left print if the
input user entered was:
1 5 -3 0
• (make a table as in the
previous example, if
uncertain)
• Can you tell what the
program does? Write
one sentence explaining
it in plane English.
Exercise 2 (on paper)
Analyze the following code. Is count<100 always
true, always false or sometimes true and
sometimes false at Point A? Answer the same
question for Point B and Point C?
8
Exercise 3 (on paper)
9
A programmer who wrote a method below thinks that the method
tests if a number is a prime. However there is a logical mistake.
1. Where is the mistake?
2. For what number does the method give a wrong answer?
3. Fix the mistake.
for loop syntax
for (; ; ) {
;
;
…
;
}
– Perform once.
– Repeat the following:
• Check if the is true. If not skip the loop.
• Execute the s.
• Perform the .
body
Exercise 4 (on paper)
How many starts does the following program
print?
11
A. 0 B. 15 C. 45 D. 48 E. 68
Exercise 5 (on paper): Nested Loops
What does the following program print?
12
Programming Exercise 1
• Design a Java program, by using do-while loop that
asks the user to enter two integers. The numbers
should be added and the sum displayed. Then the user
is asked to enter ‘Y’ if she wishes to perform the
operation again, and otherwise she enters any
character other than ‘Y’. The operation is repeated, as
long as the user chooses ‘Y’.
13
Programming Exercise 2
• Design a Java program that asks the user for two
positive integers no greater than 15 (length and width
of a rectangle). The program should then display a
rectangle of ‘*’ on the screen with the corresponding
dimensions. For example, if the user inputs width=5 and
length=3, then the program should print:
*****
*****
*****
Your program should have a method called
printRectangle that takes as input width and length and
draws the rectangle.
14
Programming Exercise 3:
Experiment with Perfect Numbers
• A positive integer is called a perfect number if it is
equal to the sum of all of its positive divisors,
excluding itself. For example, 6 is perfect number
since 6=1+2+3. The next is 28=1+2+4+7+12. There are
four perfect numbers less than 10,000. Write a
program that finds all these four numbers.
• Once you are done. Modify your program so that it looks for
all perfect numbers smaller than 35 million. What do you
notice? Assuming that you computer can do billion
instructions in a sec, can you figure out how long, roughly,
will it take your computer to find 5th perfect number (it is
33,550,336). Is the answer roughly: couple of minutes,
couple of hours, couple of days, … weeks, months, years ?
• What if you wanted to wait until it prints 6th perfect
number, which is 8,589,869,056? 15
Arrays: Prog. Exercise 4:
Fibonacci Numbers
Write a java program that creates an array containing n values
(n is 2 or greater) such that
A[0] = 1
A[1] = 1
A[i] = A[i-1] + A[i-2]
for all i in the range 1 < i < n.
– For example, the array of length 7 would be:
A = 1 1 2 3 5 8 13
• Once you are done, trace your program on paper to see what
the values in the array will be for n=5.
