Try this code:
using System;
namespace Sort3NumbersWithNestedIfs
{
class Sort3NumbersWithNetsedIfs
{
static void Main()
{
double a = double.Parse(Console.ReadLine());
double b = double.Parse(Console.ReadLine());
double c = double.Parse(Console.ReadLine());
if ((a > b) && (a > c))
{
if (b > c)
{
Console.WriteLine("{0} {1} {2}", a, b, c);
}
else
{
Console.WriteLine("{0} {1} {2}", a, c, b);
}
}
else if ((b > a) && (b > c))
{
if (a > c)
{
Console.WriteLine("{0} {1} {2}", b, a, c);
}
else
{
Console.WriteLine("{0} {1} {2}", b, c, a);
}
}
else if ((c > a) && (c > b))
{
if (a > b)
{
Console.WriteLine("{0} {1} {2}", c, a, b);
}
else
{
Console.WriteLine("{0} {1} {2}", c, b, a);
}
}
}
}
}