Lab 5 In-Class: Exploring Data Representation &
Conditional (if) Statements
- Experience the problem of overflow; gain an understanding of
why it happens and how to recognize it.
- Gain more experience with casting and widening data conversions.
- Gain experience in using if statements.
Log onto the Linux system and create a lab5 subdirectory of
directory for today's work. As usual, you will need to have three windows open:
an xterm, Emacs, and Firefox.
What is your age in seconds?
The file Age.java contains the skeleton of
a Java application that will take as input a person's age in years,
months, and days and then compute and print the age in seconds.
Complete the program as follows:
- immediately AFTER the "define conversion constants"
commment declare a conversion constant SECONDS_PER_DAY and in the
initialization have the computer do the arithmetic (in other words you
shouldn't get out your calculator and figure out how many seconds are
in a day -- write the expression so the computer has to do the work)
- define other constants and/or variables as needed
(assume there are 30 days in a month and 365 days in a year) - note
that some variables have already been declared
- calculate and print, appropriately labeled, the total number of
(place your code where indicated by the comments!!)
Test your program. For example, a person who is 18 years, 3 months, and
21 days old has lived 577,238,400 seconds (under the assumptions of the program).
A person who is 21 years, 0 months, and 0 days has lived 662,256,000 seconds.
- How many seconds has a person who is 68 years,
6 months, and 12 days old lived? Run your program to find out.
You should have gotten a strange answer to the last question!
Why did your program produce such an answer? Hint: Java uses
a 32-bit two's complement representation for type int.
So do the following to see what's going on:
- Compute the largest int value that Java can represent -
write out the formula and find its value (you can check your answer
by looking in the textbook on page 46).
- Now look at the other ages in seconds you have computed, e.g., 21 years.
68 years is a little over triple that value. So, what is the
problem with 68 years? Why did you get such a
- The above answer was clearly wrong. However, the answer can be
wrong without it being so obvious. Run the program again with an
age of 1000 years, 1 month, and 1 day. Why is this wrong?
- Fix your program as follows:
- Change the type of one variable from int to
long, which is a 64-bit integer representation.
Think about which variable is going to contain a number
too big for 32 bits - don't just randomly change! It should
work to change only ONE variable (unless you
declared lots of other variables and did several intermediate
Your program should
still work exclusively with integers, not floating point numbers.
- The above change will not completely solve the problem (run your
program and see). You need to make sure the expression is computed using
the larger data type - a carefully placed cast operator should do
the trick! (NOTE: You should be able to correct this with just one
variable type change and one cast; however, the order in which you
do calculations may require more.)
Test the program again and make sure it works. A person who has lived
68 years, 6 months, and 12 days is 2,161,036,800 seconds old.
Also try 99 years, 9 months, and 9 days and make sure the answer makes
A Base Conversion Program
In class we learned an algorithm for converting a base 10 number to another base
by repeatedly dividing by the base. Each time a division is performed
the remainder and quotient are saved.
At each step, the number used in the division is the quotient from the
preceding step. The algorithm stops when the
quotient is 0. For example to convert the base 10 number 1878 to base 8
you would do the following:
1878 divided by 8 --> 234 6
234 divided by 8 --> 29 2
29 divided by 8 --> 3 5
3 divided by 8 --> 0 3
The number in the new base is the sequence of remainders in reverse
order (the last one computed goes first; the first one goes last). In this
example, the base 8 answer is 3526 (that is 187810 = 35268).
exercise you will use this algorithm to write a program that converts a
base 10 number
to a 4-digit number in another base (you don't know enough programming yet to
be able to convert any size number). The base 10 number and the new base (2 - 9)
will be input to the program. The start of the program is in the file
BaseConvert.java. Open the file in Firefox,
save it to your lab5 subdirectory, then open it in Emacs. Modify
the program one step at a time as follows:
- The program will only work correctly for base 10 numbers that fit in
4 digits in the new base. We know that in base 2 the maximum unsigned integer
that will fit in 4 bits is 11112 which equals 15 in base 10 (or
24 - 1). In base 8, the maximum number is 77778
which equals 4095 in base 10 (or 84 - 1). In general, the
base 10 number that fits in 4 base b digits is b4 - 1.
Add an assignment statement to the program to compute this value for the
base that is input and assign
it to the variable maxNumber. Add a statement that prints out the
result (appropriately labeled). Run the program to make sure it
is correct so far.
- Now it is time to add the code to do the conversion.
The comments in the program guide you through the calculations --
place the appropriate Java statements after each comment.
Note that after each digit is calculated you concatentate it
to the variable baseBNum. This variable is a String variable that
is initially an empty string (see the instantiation already in the
code). You are "building" the string up one digit at a time.
Remember that the digits need to go in
the reverse order they are calculated (the first calculated is at the
end, the last is at the beginning).
There is already a statement to print the answer (the baseBNum variable).
- Run your program. Test it using the
following values: Enter 2 for the base and 13 for the base 10 number -- the
program should print 1101 as the base 2 value; enter 8 for the base and 1878 for
the number -- the program should print 3526 for the base 8 value; enter 3
for the base and 50 for the number -- the program should print 1212.
Adding ifs to the Base Conversion Program
Go back to your base conversion program.
- Remember that this program only computes 4 digits in the new base so if the
user enters a number that is too large to fit in 4 digits the answer produced
by the program is incorrect (it is incomplete -- it only gives the rightmost
4 digits). Unfortunately a lot of
people believe the computer so we need to be sure the computer doesn't
print out incorrect information. So do the following:
- Replace the statement that prints the
answer with an if ... else ... If the number is too large to fit in 4
digits in the new base print a message saying so (remember you calculated the
maximum number that will fit); otherwise, print the answer.
- To test
the program, use the following input: 4 for the base and 375 for the base 10
number (the program should say 375 is too big to fit in a 4-digit base 4 number);
7 for the base and 5341 for the number (again, too big); 7 for the base and
537 for the base 10 number (the program should print 1365).
- Currently the program only works for bases 2 - 9. Our next goal is to
expand it to work for bases 2 - 16. The main problem is that we must
convert the remainders larger than 9 to the appropriate letter
(10 to "A", 11 to "B", ...).
Of course the letter must be represented as a char or a String.
Modify the program as follows:
- After computing the remainder for the units place, we need to
replace the statement that concatenates the remainder to the
baseBNum variable with an
if ... else ... to
concatentate the appropriate string representation for the remainder.
Complete the following if ... else ... .
The first blank should be the condition for concatenating the
remainder as it is (that is the integer remainder is the
character added to the string)
Also include the final else
to indicate an error.
if ( _______________________________________________ )
// Concatenate the remainder with baseBNum as before
else if (remainder == 10)
// Concatenate "A" with baseBNum
else if .....
baseBNum = "Error";
- Make the appropriate modifications to find the other place
values (you can do some copying of code!).
- Run the program to make sure it works. Test the numbers you
have already tried plus try 16 for the base and 15101 for the number.
You should get 3AFD for the answer.
- Modify the original prompt so it asks for a base in the range
2 - 16.
- Modify the first if you added (the one that checks to see
if the base 10 number fits in 4 digits in the new base) so that it
first checks to make sure the base is in the correct range. The
if should do the following (you must supply the correct conditions
if the base is NOT in the range 2 - 16
print an error message telling the user the base is incorrect
else if the base 10 number doesn't fit in 4 digits
print an error message telling the user
print the number in the new base
- Test your program!! Try values such as 18, 1, 17, -2 for the base.
Final Exercise: Activities at Lake Lazydays
Implement the Lake Lazydays program from question #9 on pre-lab. That is,
write a program that prompts the user for the temperature then prints a
message suggesting the appropriate activity. Your program should
use a boolean variable for extreme temperatures and a single cascading
if statement with conditions as simple as possible (that is, don't have
unnecessary comparisons or boolean operators).
Be sure to thoroughly test your program.
To submit your code: Tar the files in your lab5 directory
(be sure to name the file with your names, not lab5.tgz)
and cp the tgz file to the directory: