我无法获得任何输出，并且我的语句因此无法正确执行，但是，每个 if 语句都会执行，即使它不应该执行？ [关闭]

Question

我想编写一个程序，将四个数字相乘并输出它们的符号，无论答案是负数还是正数。我必须使用逻辑运算符编写程序，但问题是我想先尝试使用简单的 if 语句系列，同时还要使用关系运算符。我编写了这段代码，并多次检查，代码编译并执行，但没有显示输出。它说“答案是”，后跟一个空格，并显示了我的所有 3 个 if 语句。有人可以请为我修复我的代码（并可能告诉我如何使用逻辑运算符编写这样的程序，其中我给出 4 个输入，我得到的输出说明将 4 个数字相乘后的答案是正数还是负数，如果是有什么方法可以做到这一点，而无需实际计算也就是乘法）并告诉我我的代码到底出了什么问题。代码在这里给出：

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Program746
{
    class Program
    {
        static void Main(string[] args)
        {
            int a, b, c, d;
            Console.WriteLine("Please enter the first number:");
            a = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("Please enter the second number:");
            b = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("Please enter the third number:");
            c = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("Please enter the fourth number:");
            d = Convert.ToInt32(Console.ReadLine());

            int e = a * b * c * d; 
            if (e < 0) ;
            {
                Console.WriteLine("The result is negative and has the '-' sign ");
            }

            if (e > 0) ;
            {
                Console.WriteLine("The result is positive and has the'+' sign");
            }

            if (e == 0) ;
            {
                Console.WriteLine("The result is zero, and does not have a sign");
            }
            Console.WriteLine("The answer is ", e);
            Console.ReadKey();
        }
    }
} 

Answer 1

static void Main(string[] args)
        {
            int a, b, c, d;
            Console.WriteLine("Please enter the first number:");
            a = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("Please enter the second number:");
            b = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("Please enter the third number:");
            c = Convert.ToInt32(Console.ReadLine());
            Console.WriteLine("Please enter the fourth number:");
            d = Convert.ToInt32(Console.ReadLine());

            int e = a * b * c * d;
            if (e < 0)
            {
                Console.WriteLine("The result is negative and has the '-' sign ");
            }

            if (e > 0)
            {
                Console.WriteLine("The result is positive and has the'+' sign");
            }

            if (e == 0)
            {
                Console.WriteLine("The result is zero, and does not have a sign");
            }
            Console.WriteLine("The answer is {0}", e);
            Console.ReadKey();
        }

Answer 2

删除每个 if 语句后的分号。因为最后用分号终止 if。 您可以查看此链接：https://social.msdn.microsoft.com/Forums/en-US/3508c3a2-fd1c-49db-93ea-f7bb5c2d27f4/extra-semicolon-suberst-conditional-flow?forum=csharpgeneral

你的如果：

if (e < 0) ;
{
    ...
}

如果正确：

if (e < 0)
{
    ...
}

您可以使用 i = 4 进行 for 循环，并将每个数字乘以结果 int 或将它们保存在 int 数组中，而不是使用四个 ReadLine。

我会这样写程序：

static void Main(string[] args)
    {
        int result = PrintSign(4);

        Console.WriteLine(string.Format("The answer is {0}", result));
        Console.ReadLine();
    }

    private static int PrintSign(int maxNumbers)
    {
        int result = 0;

        for (int i = 0; i < maxNumbers; i++)
        {
            int number = 0;
            while (true)
            {
                Console.WriteLine(string.Format("Please enter number {0}:", i));
                if (int.TryParse(Console.ReadLine(), out number))
                    break;
            }

            // if one number is zero, return 0 (multiply with zero and it's zero all the time)
            if (number == 0)
                return 0;
            result *= number;
        }

        // check for negative number
        if (result < 0)
            Console.WriteLine("The result is negative and has the '-' sign");
        // else, because zero is not possible at this point
        else
            Console.WriteLine("The result is positive and has the'+' sign");

        return result;
    }

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