Spring Semester 2004
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Spring Semester 2004 |
Here are examples of solutions, I skip the statement, I write only the sample solutions.
/******************************************************************************
This is the solution to the first problem in the first problem set. Note
that you need ConsoleReader, which is available from the second set of lab
notes (Lab Two) off the class notes page or from the book. Once you get the
Consolereader class off the web notes place it in a file of its own, with
the name ConsoleReader.java in the same directory with Two.java and whose
source code is written below, then compile Two.java.
*******************************************************************************/
class One {
public static void main(String[] args) {
ConsoleReader console = new ConsoleReader(System.in);
System.out.print("Please enter your first integer number, ");
System.out.println("then press Enter.");
int n1 = console.readInt();
System.out.print("Please enter your second integer number, ");
System.out.println("then press Enter.");
int n2 = console.readInt();
int sum = n1 + n2;
System.out.println(n1 + " + " + n2 + " = " + sum);
int diff = n1 - n2;
System.out.println(n1 + " - " + n2 + " = " + diff);
int prod = n1 * n2;
System.out.println(n1 + " * " + n2 + " = " + prod);
double avg = sum / 2.0;
System.out.println("avg(" + n1 + ", " + n2 + ") = " + avg);
int dist = Math.abs(n1 - n2);
System.out.println("dist(" + n1 + ", " + n2 + ") = " + dist);
long max = Math.round(avg + dist / 2.0);
// neat trick; can you explain it?
System.out.println("max(" + n1 + ", " + n2 + ") = " + max);
long min = Math.round(avg - dist / 2.0);
// neat trick; can you explain it?
System.out.println("min(" + n1 + ", " + n2 + ") = " + min);
}
}
/*****************************************************************************
This is the solution to the second problem in Lab Notes Two. ConsoleReader
is needed, use it as described in problem 2. This is a typical problem in
which you carefully need to cover roundoff errors so use Math.round after
you transform the problem in whole units (cents).
******************************************************************************/
class Two {
public static void main(String[] args) {
// get a connection to the keyboard
ConsoleReader console = new ConsoleReader(System.in);
// ask the user for the amount due
System.out.println("Type the amount due then press enter.");
// read it
double due = console.readDouble();
// ask the user for the amount received
System.out.println("Type the amount received then press enter.");
// read it
double received = console.readDouble();
// assume received is bigger than due and compute difference
double difference = (received - due);
// you need to return this as change so make it a whole number
// of cents regardless of how many decimals the user has entered
int diff = (int)(Math.round(difference * 100));
// tell the user what change you are processing
System.out.println("Give " + diff / 100.00 + " in change as follows: ");
// number of quarters; integer division
int quarters = diff / 25;
// report it
System.out.println(" " + quarters + " quarters");
// adjust the remaining change (modulo)
diff = diff % 25;
// compute the number of dimes
int dimes = diff / 10;
// report it
System.out.println(" " + dimes + " dimes");
// adjust remaining cents (notice shortcut operator)
diff %= 10; // notice anything compared to the previous assignment?
// these are the cents
int cents = diff;
// report them too
System.out.println(" " + cents + " cents");
}
}
/**********************************************************************
This is the solution to the third problem in Lab Notes Three.
Need ConsoleReader in the same directory before you can compile
it (see Lab Notes Two). Formulas used are straightforward, easy.
***********************************************************************/
class Three {
public static void main(String[] args) {
// get a connection to the keyboard
ConsoleReader console = new ConsoleReader(System.in);
// greet the user, ask for number of gallons
System.out.println("Please enter the number of gallons then press enter.");
// read number of gallons
double gallons = console.readDouble();
// ask for fuel efficiency
System.out.println("Please enter the fuel efficiency " +
"(miles/gallon) then press enter. ");
// read user input
double efficiency = console.readDouble();
// ask for price per gallon
System.out.println("Please enter the price per gallon, then press enter.");
// read price from user
double price = console.readDouble();
// computer how far the user can go with that much gas
double howFar = efficiency * gallons;
// compute how much that will cost
double totalCost = price * gallons;
// divide this by howFar and multiply by 100 to get price per 100 miles
double pricePer100Miles = totalCost / howFar * 100;
System.out.println("With the gas in the tank you can go " +
howFar + " miles, \nat a cost of " +
pricePer100Miles + " per 100 miles.");
}
}
/* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * *
This is the solution to problem four in Lab Notes Two. You need to have
ConsoleReader in a file in the same directory before you can compile and run
this. This problem adds 24 hours to the hours difference to avoid negative values
and takes the remainder with 24 to avoid values bigger than 24 (number of hours
in a day). It also transforms the hours into minutes to absorb possible negative
values from the difference between given minutes.
* * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * * */
class Four {
public static void main(String[] args) {
// get a connection to the keyboard
ConsoleReader console = new ConsoleReader(System.in);
// greet the user, ask for time
System.out.print("Please enter the first time: ");
// get the first time as a string (in military format)
String first = console.readLine();
// compute the number of hours from first two characters
int hours1 = Integer.parseInt(first.substring(0, 2));
// compute minutes from next two characters
int minutes1 = Integer.parseInt(first.substring(2, 4));
// ask for second time
System.out.print("Please enter the second time: ");
// get it
String second = console.readLine();
// compute hours, same as before
int hours2 = Integer.parseInt(second.substring(0, 2));
// compute minutes
int minutes2 = Integer.parseInt(second.substring(2, 4));
// compute the difference between hours, add 24 then divide
// by 24 and take the remainder to express the hour difference
int difHours = (hours2 + 24 - hours1) % 24;
// make these hours into minutes
int hrsToMins = difHours * 60;
// compute straight difference between given minutes, could be < 0
int difMins = minutes2 - minutes1;
// add this to total count of minutes
hrsToMins += difMins;
// report total count of minutes in hours and minutes
System.out.println(
hrsToMins / 60 + " hours " + hrsToMins % 60 + " minutes"
);
}
}
/*******************************************************************************
This is the solution to problem number five in the first problem set.
The program attempts to use a different way of computing the average of
two numbers a and b by computing (1/a + 1/b)*a*b/2 in stages. It is OK if
the numbers entered are restricted to integers, but to correctly compute
at all stages in the program we need to circumvent integer division which
can result in a loss of precision. So we turn everything in float and all
is well after that. You need ConsoleReader as explained above.
********************************************************************************/
class Five {
public static void main(String[] args) {
ConsoleReader console = new ConsoleReader(System.in);
// one change below
float total = 0;
System.out.println("Please enter a positive number:");
// second change below
float x1 = (float)Integer.parseInt(console.readLine());
System.out.println("total = " + total);
total = total + 1 / x1;
System.out.println("total = " + total);
System.out.println("Please enter a positive number:");
// third change below
float x2 = (float)Integer.parseInt(console.readLine());
total = total + 1 / x2;
System.out.println("total = " + total);
total = total * x1 * x2 / 2;
System.out.println("total = " + total);
System.out.println("The average is " + total);
// that's it, three changes overall
}
}
/***********************************************************************************
Solution to problem six in the first problem set. Use ConsoleReader from lab
notes as explained in problem set 2. The trick here (as hinted in the text) is
to transform a number for a month in the position in the string where the month
name is starting, all names being made of the same length, and then concatenated
together in one final string.
************************************************************************************/
class Six {
public static void main(String[] args) {
String monthNames = "January " +
"February " +
"March " +
"April " +
"May " +
"June " +
"July " +
"August " +
"September " + // longest
"October " +
"November " +
"December " ;
// open a connection with the keyboard
ConsoleReader console = new ConsoleReader(System.in);
// greet the user, and ask for input
System.out.println("Please enter a month number from 1 to 12.");
// get month name
int month = console.readInt();
// report the name of the month
System.out.println(
monthNames.substring("September ".length() * (month-1),
"September ".length()*month));
// formula uses the length of the longest name
}
}