Java program to calculate the combinations function

问题

For my programming class I have to make a program that calculates the combinations function C(n,k) = n!/(k!*(n-k)!) by using a main method to deal with input/output, a method to compute the factorial, and a method to compute the combinations function. Here's my code:

import java.util.Scanner;
public class Combinations {

    public static void factorials (int set, int objects) {
        Scanner keyboard = new Scanner(System.in);
        int n = set;
        int k = objects;
        int c = (n-k);
        int factorial1 = 1;
        int factorial2 = 1;
        int factorial3 = 1;
        while (n > 0) {
            factorial1 = factorial1 + s;
            n = n++;
        }//while loop
        while (k > 0) {
            factorial2 = factorial2 + o;
            k = k++;
        }//while loop
        while (c > 0) {
            factorial3 = factorial3 + c;
            c = c++;
        }//while loop
        System.out.println(Combinations(factorial1,factorial2,factorial3));
    }//method factorials
    public static int Combinations (int set, int objects, int x){
        int n = set;
        int k = objects;
        int c = x;
        int combination;
        combination = n/(k*c);
        return combination;
    }//method Combinations
    public static void main(String[] args) {
        Scanner keyboard = new Scanner(System.in);
        System.out.println("Enter the number of integers in a set: ");
        int n = keyboard.nextInt();
        System.out.println("Enter the number of objects to be chosen from the set: ");
        int k = keyboard.nextInt();
        System.out.println(factorials(n,k));
    }//method main

}//class

My problem is that I'm getting an error message for System.out.println(factorials(s,o)); - "The method println(boolean) in the type PrintStream is not applicable for the arguments (void)". I have no idea why it's saying this. Help?

回答1:

In your code,

public static void factorials(int set, int objects)
{
}

returns void. you cannot use void method in System.out.println(factorials(s, o));

try chaning your code as

public static int factorials(int set, int objects)
{
}

another way to calculate combinations without method calling,

        int index, numberOfItems, itemsToBeSelected, combinations;
        int factorial, temp, result;

        Scanner scanner = new Scanner(System.in);
        System.out.println("Number Of Items (n) : ");
        numberOfItems = scanner.nextInt();

        System.out.println("Items to be selected (r): ");
        itemsToBeSelected = scanner.nextInt();


        for (index = 1, factorial = 1; index <= numberOfItems; index++)    /* Calculate (numberOfItems) -> n! */
        {
            factorial = factorial * index;
        }

        for (index = 1, temp = 1; index <= itemsToBeSelected; index++)         /* Calculate (itemsToBeSelected) -> r! */
        {
            temp = temp * index;
        }

        for (index = 1, result = 1; index <= (numberOfItems - itemsToBeSelected); index++) /* Calculate (numberOfItems - itemsToBeSelected) -> (n-r)!*/
        {
            result = result * index;
        }

        combinations = factorial / (temp * result);
        System.out.println("Combinations : " + numberOfItems + "C" + itemsToBeSelected + " : " + combinations);

Output:

Number Of Items (n) : 
8
Items to be selected (r): 
3
Combinations : 8C3 : 56

回答2:

Basically you are passing an argument to your println(Object) method. But factorials(s,o) returns a void. You can either call println() or else if you want to use println(Object) then factorials(s,o) should return a descendent of java.lang.Object.

Refer to specifications for further understanding :

PrintStream

来源：https://stackoverflow.com/questions/19532553/java-program-to-calculate-the-combinations-function

标签

java

methods

combinations

factorial