Help with repetition/iteration/loops

[Victoria_1]

For a homework assignment in my intro to java class I was given the following problem:

Write for, do-while, and while statements to compute the following sum and product
1. 1 + 7 + 25 + 79 + .... + (3^20 - 2)
2. 1 x 3 x 9 x 27 x 81 x ... x (3^20)

I understand how to write the statements, I'm just not sure how to express the increment.
For the first one (for statement) I have

int i, sum = 0;
            for (i = 1; i =< 2486784399; // I'm not sure what would go here ) {
                sum += i;

                                ]

            System.out.println(“The sum is” + sum); 

I'm not sure how to show that it's increasing by 3^(n) - 2

[Proxet]

Have a look at this post, maybe it will help you :) Click Here

[cmps]

Hello Victoria_1 and welcome to programming in Java :)
The "For loop" has the following form:
for(int i = 0; i < NUMBER; i++)
for(initialize i to a number; compare i with NUMBER; increment i by 1)
i++ is the same as i = i + 1
So if you want to increment i by 10 for example, you would write
i = i + 10 rather than i++

GL

[zolymo]

Sorry for the delay, answer is here ;)
u can change another value for number and potency, in this example is
number= 3 (number = 2 - in a second example)
potency = 20 (potency = 5 -in a second example)
Class LoopsSolution:

package daniweb;

import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;

/**
 *
 * @author JoZulyk http://inovawebstudio.com
 */
public class LoopsSolution {
/*
    For a homework assignment in my intro to java class I was given the following problem:

Write for, do-while, and while statements to compute the following sum and product
1. 1 + 7 + 25 + 79 + .... + (3^20 - 2)
2. 1 x 3 x 9 x 27 x 81 x ... x (3^20)

I understand how to write the statements, I'm just not sure how to express the increment.
For the first one (for statement) I have
    */
    public static List<Double> numGenerator(int number, int potency){
        //number is in this case 3, repetition is in this case 20 (0-20)
        List<Double> numbersGenerated = new ArrayList<>();
        for(int i= 0; i<= potency; i++){
            numbersGenerated.add(Math.pow(number, i));
        }
        return numbersGenerated;
    }
    public static String sumFuntionStringGenerator(List<Double> numsGenerated){
        String sum = "";
        Iterator it = numsGenerated.iterator();
        while(it.hasNext()){
            Double num = (double)it.next();
            if(num!=1d)
            sum += (num - 2) + " + ";
        }
        return sum;
    }
    public static String productFuntionStringGenerator(List<Double> numsGenerated){
        String prod = "";
        Iterator it = numsGenerated.iterator();
        while(it.hasNext()){
            Double num = (double)it.next();
            prod += num + " * ";
        }
        return prod;
    }
    public static void main(String [] argv){
        //here u can change for an different value ;)
        int number = 3;
        int potency = 20;
        List<Double> numbers = numGenerator(number,potency);
        //obtaining the sum: 1. 1 + 7 + 25 + 79 + .... + (3^20 - 2)
        //are:  (3^1 - 2) + (3^2 - 2) +  (3^3 - 2)+...+ (3^20 - 2)
        double sum = 0;
        Iterator it = numbers.iterator();
        while(it.hasNext()){
            Double num = (double)it.next();
            //skipping the first term because (3^0 - 2) doesn't apply
            if(num != 1d){ 
                sum = sum + num - 2;
            }
        }
        System.out.println("Sum function is: " + sumFuntionStringGenerator(numbers) );
        System.out.println("Result are: " + sum);

        //obtaining the product: 2. 1 x 3 x 9 x 27 x 81 x ... x (3^20)
        //are:  (3^0) + (3^1) +  (3^2)+...+ (3^20)
        double prod = 1; 
        Iterator pit = numbers.iterator();
        while(pit.hasNext()){
            Double num = (double)pit.next();
            prod *= num;
        }
        System.out.println("Product function is: " + productFuntionStringGenerator(numbers) );
        System.out.println("Result are: " + prod);

    }
}

the output are:

Sum function is: 1.0 + 7.0 + 25.0 + 79.0 + 241.0 + 727.0 + 2185.0 + 6559.0 + 19681.0 + 59047.0 + 177145.0 + 531439.0 + 1594321.0 + 4782967.0 + 1.4348905E7 + 4.3046719E7 + 1.29140161E8 + 3.87420487E8 + 1.162261465E9 + 3.486784399E9 + 
Result are: 5.23017656E9
Product function is: 1.0 * 3.0 * 9.0 * 27.0 * 81.0 * 243.0 * 729.0 * 2187.0 * 6561.0 * 19683.0 * 59049.0 * 177147.0 * 531441.0 * 1594323.0 * 4782969.0 * 1.4348907E7 * 4.3046721E7 * 1.29140163E8 * 3.87420489E8 * 1.162261467E9 * 3.486784401E9 * 
Result are: 1.5684240429131528E100

...
output for the seconde values:

Sum function is: 0.0 + 2.0 + 6.0 + 14.0 + 30.0 + 
Result are: 52.0
Product function is: 1.0 * 2.0 * 4.0 * 8.0 * 16.0 * 32.0 * 
Result are: 32768.0

its all ;), please mark this post how SOLVED! ... have a great day!

[stultuske]

zolymo: please, try not to provide custom made code. they won't learn anything this way.
why should this thread be marked 'solved' ? because you posted your code ?

[zolymo]

i post an question! and i think if i help ! i obtain help too. sorry.

[stultuske]

that's the point exactly, you aren't helping.
This is like scripture saying: "give a man a fish, and he'll eat for a day. teach a man to fish, and he'll never get hungry again."

teach him how to solve his problem, don't just provide copy-paste ready code.