Check if a year is Leap or not and save it in an Array, then Print those that are Leap and those that are not

You have to take the variable out of the for and initialize it, because it may not enter the for and it would never be initialized and that is the error that can occur and the visual studio marks you.

        Console.WriteLine("Parcial #2 - Jesus Palma");
        Console.WriteLine("------------------------");
        Console.WriteLine(" ");
        Console.WriteLine("Clasificación de año bisiesto y no bisiesto. \n");
        Console.Write("¿Cuántos años desea ingresar para clasificar?: ");
        op = Int32.Parse(Console.ReadLine());
        Console.Write("\n");

        anoBisiesto = new int[op]; // fuera del for, y queda disponible para todo el metodo.

        for (i = 0; i < op; i++)
        {
            anoNoBisiesto = new int[op];

            Console.Write("Ingrese un año: ");
            año = Int32.Parse(Console.ReadLine());

            if (año % 4 == 0 && (año % 100 != 0 || año % 400 == 0))
            {
                Console.WriteLine("El año " + año + " Si es bisiesto \n");
                anoBisiesto[op] = año;

            }
            else
            {

                Console.WriteLine("El año " + año + " No es bisiesto \n");
                anoNoBisiesto[op] = año;
            }
        }

        for (i = 0; i < op; i++)
        {

            Console.WriteLine("DATOS DEL VECTOR: ");
            Console.WriteLine("--------------------- \n");
            Console.Write("" + anoBisiesto[op] + " ");
        }

The answer was quite simple, for the dimension of the array, when "How many years" we want to enter is displayed, they are stored in the variable op, then, I equal it numeroswith op, and the Array (Array) I declare it as an integer in the following way: int[] añosBisiestos = new int[numeros];and the other int[] añosNoBisiestos = new int[numeros];, what this does is that the LeapYears and NonLeapYears Arrays have as dimension the number of years to be entered, and, if it is a leap year, añosBisiestos[i] = año;the year is stored inside the array añosBisiestoand inside this, the ito indicate the position of the year, for example: LeapYears[0], LeapYears[1], etc, and at the end, to display the data stored in the array, a cycle identical to the first is made and the array is printed:Console.Write("[" + añosBisiestos[i] + "] \n");

Código final abajo:

using System;

namespace parcial2JesusPalma
{
    class Program
    {

        static void Main(string[] args)
        {
            int año, op, i, numeros;


            Console.WriteLine("Parcial #2 - Jesus Palma");
            Console.WriteLine("------------------------");
            Console.WriteLine(" ");
            Console.WriteLine("Clasificación de año bisiesto y no bisiesto. \n");
            Console.Write("¿Cuántos años desea ingresar para clasificar?: ");
            op = Int32.Parse(Console.ReadLine());
            numeros = op;

            int[] añosBisiestos = new int[numeros];
            int[] añosNoBisiestos = new int[numeros];

            Console.Write("\n");

            for (i = 0; i < numeros; i++)
            {

                Console.Write("\n Ingrese un año: ");
                año = Int32.Parse(Console.ReadLine());


                if (año % 4 == 0 && (año % 100 != 0 || año % 400 == 0))
                {
                    
                    añosBisiestos[i] = año;
                    Console.WriteLine("El año " + año + " Si es bisiesto");
                }

                else
                {
                    
                    añosNoBisiestos[i] = año;
                    Console.WriteLine("El año " + año + " No es bisiesto");
                }

            }
            
            Console.WriteLine("\n DATOS INGRESADOS: \n");
            for (i = 0; i < numeros; i++)
            {
                Console.WriteLine("AÑOS BISIESTOS INGRESADOS: \n");
                Console.Write("[" + añosBisiestos[i] + "] \n");
                Console.WriteLine("AÑOS NO BISIESTOS INGRESADOS: \n");
                Console.Write("[" + añosNoBisiestos[i] + "] \n");
            }
            Console.ReadKey();
        }
    }
}

I propose an alternative, you could use the IsLeapYear function that belongs to the DateTime class , this function returns true if the year is a leap year and false otherwise. And also use Linq .

int año, op;

Console.WriteLine("Parcial #2 - Jesus Palma");
Console.WriteLine("------------------------");
Console.WriteLine(" ");
Console.WriteLine("Clasificación de año bisiesto y no bisiesto. \n");
Console.Write("¿Cuántos años desea ingresar para clasificar?: ");
op = Int32.Parse(Console.ReadLine());
Console.Write("\n");
int[] arregloAños = new int[op];

for(int i = 0; i < op; i++)
{
   Console.Write("Ingrese un año: ");
   año = Int32.Parse(Console.ReadLine());
   arregloAños[i] = año;
}

So far, what we have done is declare an array of years which will save us all the years that we enter, regardless of whether or not it is a leap year.

We will now use Linq to determine which years are leap years and which years are not.

var bisiestos = (from a in arregloAños
                 where DateTime.IsLeapYear(a)
                 select a).ToArray();

Console.WriteLine("Años bisiestos");

foreach(var b in bisiestos)
{
    Console.WriteLine(b.ToString());      
}

Here what is done is a Linq query , which will go through all the years of the original array and will ask if each year is a leap year, returning an array with all the leap years.

Subsequently, through a foreach , all the elements of the leap array are traversed and they are printed on the console.

For non-leap years it would be similar:

var noBisiestos = (from a in arregloAños
                   where DateTime.IsLeapYear(a) == false
                   select a).ToArray();

Console.WriteLine("Años no bisiestos");

foreach(var b in noBisiestos)
{
    Console.WriteLine(b.ToString());      
}

This time the Linq query will return the non-leap and we print them using a foreach as well .

To use Linq you must put in the usings:

using System.Linq;