如何制作一個將兩個以上數字相乘的計算器？

Question

我做了一個計算器，它可以做多種事情（添加連續數字，添加多個數字等），但我無法制作它，以便計算器可以乘以多個數字。 到目前為止，我基本上復制了將多個數字相加的代碼，但我不知道如何讓它相乘而不是相加。

這是我的代碼：

import java.util.Scanner;

public class SumOfNumbers {
public static void main(String arg[])
{
int n;
int sum = 0;

Scanner s = new Scanner(System.in);

System.out.print("Please enter how many numbers you want to add up to: ");
n = s.nextInt();

System.out.println("you entered: " + n + "");
sum = addConsecutiveNumbers(n);

System.out.println("sum of 1 to "+n+" = "+sum);



//following code is sum of any numbers you entered from console
//store the numbers into an array
int num;
int sumOfNums=0;

System.out.print("Please enter how many numbers you want to sum: ");
num=s.nextInt();
System.out.println("you want to sum "+num+" numbers ");

sumOfNums = addNumbers(num);

System.out.println("sum of "+num+" numbers = "+sumOfNums);
}



//Define a method which add consecutive numbers based on user's input and return the sum of the numbers
private static int addConsecutiveNumbers (int number)
{
int sum = 0;
for (int i = 1; i <= number; i++)
{
sum = sum + i;
}

return sum;

}


//Define a method which add numbers based on user's input and return the sum of the numbers

private static int addNumbers (int num)
{
Scanner s = new Scanner(System.in);
int a[] = new int[num];
int sumOfNums = 0;

for(int k = 0; k < num; k++)
{
System.out.println("enter  number  "+(k+1)+":");
a[k] = s.nextInt();

System.out.println("The array of a[" + k + "] = " + a[k]);
}

for(int j = 1;j < num ; j++)
{
sumOfNums += a[j];
}

return sumOfNums; 
}
//below is the part of code that I am having trouble with.

public static int multiplyNumbers(int num)
{
    int Area = 0; 
    Scanner s = new Scanner(System.in);
    int a[] = new int[num];
    System.out.println("Please enter how many numbers you want to multiply:");
    num=s.nextInt();
    for(int l = 0; l < num; l++)
    {
    System.out.println("enter  number  "+(l+1)+":");
    a[l] = s.nextInt();
    System.out.println("The array of a[" + l + "] = " + a[l]);
    }
    return Area;
}
}

Answer 1

您不需要將值存儲在數組中進行乘法類似的加法，您可以直接更新最終結果

    public static int multiplyNumbers(int num) {
        int Area = 1;
        Scanner s = new Scanner(System.in);
        System.out.println("Please enter how many numbers you want to multiply:");
        num = s.nextInt();
        for (int l = 0; l < num; l++) {
            System.out.println("enter  number  " + (l + 1) + ":");
            int temp = s.nextInt();
            Area *= temp;
            System.out.println("The array of a[" + l + "] = " + temp);
        }
        return Area;
    }

Answer 2

我馬上看到一件事； 我看到你的代碼的方式，以下兩行是多余的：

System.out.println("Please enter how many numbers you want to multiply:");
num=s.nextInt();

您應該已經詢問用戶他們想要乘以多少個數字，因為它是作為參數傳入的。 至於您的實際問題，請查看addNumbers()方法中的這些行：

for(int j = 1;j < num ; j++)
{
sumOfNums += a[j];
}

您所要做的就是在您的退貨聲明（ return Area; ）之前復制該代碼。 您需要對其進行一些調整，以便它不使用sumOfNums變量，而是使用Area變量，而不是相加，而是相乘。 這可以這樣做：

for(int j = 0;j < num ; j++) //j also needs to start at 0, I think you may have made a mistake when writing the summing method
{
Area *= a[j];
}

你會注意到這個算法有一個問題（我自己幾乎沒有發現）。 Area以 0 值開始，因此 0 乘以任何數字將始終為 0。簡單修復； 只需手動將Area設置為循環前的第一個值。 像這樣的東西：

Area = a[0];
for(int j = 1; j < num; j++)
{
sumOfNums += a[j];
}

另請注意，這次我在j = 1處開始了 for 循環。 這是因為我已經開始Area作為a[0] ，所以我們不想將該數字乘以兩次。