<分区>
基本上我正在编写一个计算三角形面积的小程序。但是，即使我输入正数，我也会收到该数字为负数的警告。在我添加负数检查之前它起作用了。谁能帮帮我？
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace ConsoleApplication5
{
class Program
{
static void Main(string[] args)
{
double num;
Console.WriteLine("Base length: ");
num = Convert.ToDouble(Console.ReadLine());
if (num < 0 );
{
Console.WriteLine("The number cannot be negative");
Console.ReadKey();
return;
}
double num2;
Console.WriteLine("Height: ");
num2 = Convert.ToDouble(Console.ReadLine());
if (num2 < 0) ;
{
Console.WriteLine("The number cannot be negative");
Console.ReadKey();
return;
}
double x = num;
double y = num2;
Console.WriteLine("Base is " + x + "cm long, and the height is " + y + "cm");
Console.WriteLine("1/2*" + x + "*" + y);
Console.WriteLine("The area is " + 0.5*x*y + "square cm.");
Console.ReadKey();
}
}
}