what is #if in c code example

Example 1: c# if statement

using System;
namespace DecisionMaking 
{
   class Program 
   {
      static void Main(string[] args) 
      {
         /* local variable definition */
         int a = 10;
        
         /* check the boolean condition using if statement */
         if (a < 20) 
         {
            /* if condition is true then print the following */
            Console.WriteLine("a is less than " + a); //output: a is less than 20
         }
         Console.ReadLine();
      }
   }
}

Example 2: if c#

int time = 22;
if (time < 10) 
{
  Console.WriteLine("Good morning.");
} 
else if (time < 20) 
{
  Console.WriteLine("Good day.");
} 
else 
{
  Console.WriteLine("Good evening.");
}