I am new to using java and am having some issues in my java class right now and will be needing help with my specific code. I try to look at others questions on here all the time but it's never exactly what I need. Here are my directions:
Create a Java file called CompoundInterestYourLastName. Write a method called computeBalance() that computes the balance of a bank account with a given initial balance and interest rate, after a given number of years. Assume interest is compounded yearly.
Use a loop to control the iterations through the years in your method.
Your method should return a double value.
In your main method, run the following tests to verify your method is working correctly.
System.out.printf("Your total is $%.2f", computeBalance(1000, .045, 3));
// should return $1141.17
I am using eclipse and my only current error is in the comments. I also want some general tips and let me know if my logic is wrong. It probably is. :D
Here is what I have currently although I have been trying different things:
import java.util.Scanner;
import java.lang.Math;
public class CompoundInterestTidwell {
public static void main(String[] args) {
double compInt = computeBalance(1000, 0.045, 3);
System.out.printf("Your new balance is $%.2f", compInt);
}
// Getting arror for line of code below.
// Error: This method must return a result of type double
public static double computeBalance(int P, double r, int t) {
// Formula for compounding interest
// A = P(1+(r/n))^(n(t))
// The examples to check my math had rate already divided by 100 so I left out r/n.
for(int c = 0; c <= t; c++ ) {
// deleted 'n' from equation because it need to equal 1 anyways.
double compInt = Math.pow(P*(1+r), t);
if (c < t) {
c++;
return compInt;
}
}
}
}
Thanks.
Your function computeBalance doesn't guarantee to return a value, because the only return statement is in an if clause, within a loop (making it two conditions deep).
This is a thing the compiler is warning you about. Basically it scans your code and makes sure that a function declared as double will actually return a valid value of type double and so on.
If you add a return statement at the end of the body in the function (or throw an error) it should compile.
I am not exactly sure what your function does in technical terms, but I've rewritten it so it should return the same value, but should now actually compile.
public static double computeBalance(int P, double r, int t) {
// Formula for compounding interest
// A = P(1+(r/n))^(n(t))
// The examples to check my math had rate already divided by 100 so I left out r/n.
double compInt = 0; // Declare compInt outside the loop.
for(int c = 0; c <= t; c++ ) {
// deleted 'n' from equation because it need to equal 1 anyways.
compInt = Math.pow(P*(1+r), t);
if (c < t) {
c++;
break; // Break instead of return, will immediately
// go to the return statement outside the loop.
}
}
return compInt; // Moved the return statement to outside the loop so
// the function always will return a double.
}
Related
In this code, I've used a global variable to increase the value of p whenever control touches the base case. But I want to do it without using a global variable. Is that possible?
public class stairCase {
static int p=0;
public static void main(String[] args) {
// TODO Auto-generated method stub
int n = func(14,0);
System.out.println(n);
}
public static int func(int n, int c){
if(n==c){
p++;
return 1;
}
if(n-c>=1){
func(n,c+1);
}
if(n-c>=2){
func(n,c+2);
}
if(n-c>=3){
func(n,c+3);
}
return p;
}}
Your problem is that you're throwing away a major communication resource: the return value. You recur in three places, but ignore the value. Harness that, and you'll solve your problem.
Consider something like this:
if (n < c) return 0 // Jumping too far gives no solution
else if (n == c) return 1 // Jumping to the top step is 1 solution
else
return func(n, c+1) + // Other jumps: sum the solutions from
func(n, c+2) + // each of the reachable steps.
func(n, c+3)
For future programming, please learn about useful variable names and documentation. I would not have followed this decently, had I not solved this problem yesterday in another posting.
You can do a little better with this problem if you reverse your counting. Note that you never change n as you recur -- in that case, why pass it at all? Start c at 14 and count to step 0 (the top).
Converting the code is left as an exercise for the student. :-)
I tried to write code to get the largest prime factor of a big number (in this case, 600851475143).
After writing four different methods (2 to show results, and 2 with other calculations), I have written the program class, and tried to run it.
When I run it, the result should appear in the console, but nothing shows up. I tried to make the variable that should be printed public, and just print it manually, but it didn't work. Eventually, I wrote the simplest System.out.print() command in the main method, but nothing appeared in the console.
I have no idea what the problem is. Does anyone here have a clue?
The class:
public class Problem3 {
public float sum1;
public float sum2;
private float num = 600851475143f;
public void methodGuy(){
while(sum1==0){
for(int i=2; i<num/2; i++){
if(num%i==0){
sum1=num/i;
} else {}
}
}
}
public void show1(){
System.out.println("the result of Guys method is: " + sum1);
}
public void methodOr(){
for(int i=2; i<num/2; i++){
for(float x=num/2; x>2; x=x-1){
if(i*x==num){
sum2=x;
}
}
}
}
public void show2(){
System.out.println("the result of Ors method is: " + sum2);
}
}
The program class:
public class Program {
public static void main(String[] args) {
Problem3 x = new Problem3();
x.methodGuy();
x.show1();
x.methodOr();
x.show2();
}
}
methodGuy will never terminate because int's can't get that big.
The largest possible value of an int is 2147483647. If your int is that number, and you add one to it, the number will wrap around and become negative. So after i++, the next value will be -2147483648. Since the loop will continue as long as i is less than 600851475143/2 = 300425237071.5, and since i will always be less than that, your loop is infinite.
Best would be to make both i and num have type long, instead of int or float. Even if you do that, your loop will probably run for a very long time.
In fact, if there are no factors, the loop will be infinite, because sum will never be set to something other than 0, and then since you say while (sum==0), the loop will just start over again and do the same thing infinitely. So aside from the wraparound problem, your algorithm still needs work.
Further note: You definitely do not want to use float for this, because the number 600851475143 cannot be represented exactly. The actual value of num will be 600851480576.
I already searched everywhere for a solution for my problem, but didn't get one. So what I'm trying to do ist use recursion to find out whats a passed integer variable's base to the power of the passed exponent. So for example 3² is 9. My solution really looks like what I found in these forums, but it constantly gives me a stack overflow error. Here is what I have so far.(To make it easier, I tried it with the ints directly not using scanner to test my recursion) Any idea?
public class Power {
public static int exp(int x,int n) {
n = 3;
x = 2;
if (x == 0) {
return 1;
}
else {
return n * exp(n,x-1);
}
}
public static void main(String[] args) {
System.out.println(exp(2,3));
}
}
Well, you've got three problems.
First, inside of the method, you're reassigning x and n. So, regardless of what you pass in, x is always 2, and n is always 3. This is the main cause of your infinite recursion - as far as the method is concerned, those values never update. Remove those assignments from your code.
Next, your base case is incorrect - you want to stop when n == 0. Change your if statement to reflect that.
Third, your recursive step is wrong. You want to call your next method with a reduction to n, not to x. It should read return x * exp(x, n-1); instead.
This was my answer to a question in which I was supposed to convert an iterative method to a recursive method. The teacher told me I cant use a-=1 as a parameter... So they gave me 0 points..
When I run this it works as it supposed to be..
Could someone tell me why its wrong?
public int do(int a){
if(a==0){
return 1 ;
}else{
return a * do(a-=1);
}
}
The problem with your code is that you're reading the value of a and reassigning it with a -= 1 in the same expression, but the order of these operations is not specified. The statement:
return a * do(a -= 1);
could be implemented as:
temp = a;
a -= 1;
return temp * do(a);
which will do what you were probably expecting, or:
a -= 1;
return a * do(a);
which will multiply by the decremented value of a rather than its original value.
The correct way to write your function is:
public int do(int a){
if(a==0){
return 1 ;
}else{
return a * do(a-1);
}
}
Just pass the result of the subtraction as an argument, don't reassign the variable at the same time.
I assume that this is in java?
I see two big problems with this snippet.
do is a reserved keyword. It may cause compilation errors, so you should name your method something else.
Executing -= in a parameter call seems quite ambiguous. Will the negation operator run before or after the multiplication by a? The more clear operator to use would be simply the - operator, and it would complete with the same result.
That said, something like this might have been what the teacher was looking for:
public int calculateSomething(int a) {
if (a == 0) {
return 1;
} else {
return a * calculateSomething(a - 1);
}
}
I'm starting to get blind looking at my code and my brain is about to overheat. I'm new when it comes to programming.
public class RecyclingSystem {
public static void main(String[] args) {
System.out.println("Please put in a valid bottle");
Scanner sc = new Scanner(System.in);
while ( sc.nextInt() != -1) {
if (sc.nextInt(char a) = getaBottle);
int bottleAcount++;
} else if { (sc.nextInt(char b) = getbBottle);
int bottleBcount++;
} else if { (sc.nextInt(char c) = getcBottle);
int bottleCcount++;
} else { throw new EmptyStackException();
System.out.println("Bottle not recognized");
}
System.out.println("The total number of bottles is " + totalBottlecount);
System.out.println();
System.out.println("The total amount returned is " + sumOfBottles );
}
sc.close();
}
}}
public class Bottle {
private static final double A_BOTTLE = 1.0;
/**
* #return the aBottle
*/
public static double getaBottle() {
return A_BOTTLE;
}
/**
* #return the bBottle
*/
public static double getbBottle() {
return B_BOTTLE;
}
/**
* #return the cBottle
*/
public static double getcBottle() {
return C_BOTTLE;
}
private static final double B_BOTTLE = 1.5;
private static final double C_BOTTLE = 3.0;
}
public class EmptyStackException extends Exception {
}
public class bottleCount {
int bottleAcount = 0;
int bottleBcount = 0;
int bottleCcount = 0;
int totalBottleCount = bottleAcount + bottleBcount + bottleCcount;
}
I have seperate classes for the getbottle, totalBottlecount and bottlecount variables.
I want to make a user-input based recycling system simulator, if that makes any sense, with 3 different types of bottles, which are assigned different values, a total bottle count and the sum of the values of the 3 bottle types combined.
I get several compiler errors and I have spend HOURS trying to resolve them all, but every time I do, new errors occur and now I get a "coders-block".
I get asked to delete the ++ tokens, the compiler cannot resolve my variables and syntax errors. I would really appreciate some insight, since I'm only ~3weeks into java programming.
UPDATED: Compiler errors exact copy pasta
Multiple markers at this line
- Syntax error, insert ")" to complete Expression
- Duplicate method nextInt(char) in type RecyclingSystem
- Syntax error, insert "}" to complete Block
- Syntax error, insert "AssignmentOperator Expression" to complete Assignment
- Return type for the method is missing
- Syntax error on tokens, delete these tokens
- The left-hand side of an assignment must be a variable
- Syntax error, insert "AssignmentOperator Expression" to complete Expression
- The left-hand side of an assignment must be a variable
- Syntax error, insert ";" to complete BlockStatements
- Syntax error on tokens, delete these tokens
- Syntax error on token ")", { expected after this token
- Syntax error, insert ";" to complete Statement
int bottleAcount++;
In java you need to declare the local variable like
type name = intial value;
then do any operation on that like increament or decrement.
In youe case declar the variable before while loop with zero as intial value like
int bottleAcount = 0;
then inside while increament it by 1, like bottleAcount++;
or
bottleAcount += 1;
So... If this is all the code there are many problems and what can I recommend in the beginning - go back to some basic Java programming course.
Let's look at one of the first lines:
if (sc.nextInt(char a) = getaBottle);
Firstly, it's a condition, and you are assigning the value of a getaBottle to the sc.nextInt(char a).
Secondly, nextInt(char a) looks like method declaring, not like a method call.
Thirdly, getaBottle is never declared before
Fourthly, you have a getaBottle() method in a Bottle class, which you probably want to use instead of getaBottle which is (should) be a variable
...etc., etc.
This code is not even valid Java code. It's hard to help you somehow in that problem, you just need to learn a bit more, which I encourage you to do.
Good luck and in case of any specific question - come and ask!
else if { (sc.nextInt(char b) = getbBottle);
int bottleBcount++;
}
Syntax is totally wrong for if.Also condition is checked using == not = It should be :
else if (sc.nextInt(char b) == getbBottle);
int bottleBcount++;
Also you cant do int bottleBcount++. Its meaningless. Since you already declared bottleBcount in another class, you have to access it using the object of that class. Before that change the declaration in the class from int bottleAcount = 0; to public int bottleAcount = 0; . Do this for all bottles.
Now you can use it as :
public static void main(String[] args) {
System.out.println("Please put in a valid bottle");
bottleCount counter = new bottleCount();
Scanner sc = new Scanner(System.in);
while ( sc.nextInt() != -1) {
if (sc.nextInt(char a) == getaBottle);
counter.bottleAcount++;
} else if (sc.nextInt(char b) == getbBottle);
counter.bottleBcount++;
else if (sc.nextInt(char c) == getcBottle);
counter.bottleCcount++;
else { throw new EmptyStackException();
System.out.println("Bottle not recognized");
}
System.out.println("The total number of bottles is " + totalBottlecount);
System.out.println();
System.out.println("The total amount returned is " + sumOfBottles );
}
sc.close();
}
Also the statement int totalBottleCount = bottleAcount + bottleBcount + bottleCcount; doesnt make sense. It won't work as you wanted it to. You need to write a function to do this addition and then call it. Or if you want this to happen just once ( which I doubt) , you can put it in a constructor.
I suggest you brush up on class and variable declaration concepts before proceeding
You just have problem in this:
else {
throw new EmptyStackException();
System.out.println("Bottle not recognized");
}
Check the proper syntax and error will be resolved.