Demo: Dictionary

using System;
using System.Collections.Generic;

namespace DemoDictionary
{
    internal class Program
    {
        static void Main(string[] args)
        {
            //ученик -> оценка
            Dictionary<string, double> students = new Dictionary<string, double>();
            students.Add("Pesho", 5.60);
            students.Add("Niki", 3.40);
            students.Add("Ivan", 5.40);
            //Pesho -> 5.60
            //Niki -> 3.40
            //Ivan -> 5.40
            students.Remove("Ivan");
            //Pesho -> 5.60
            //Niki -> 3.40

            Console.WriteLine(students.ContainsKey("Desi")); //False
            Console.WriteLine(students.ContainsKey("Pesho")); //True

            Console.WriteLine(students.ContainsValue(3.40)); //True
            Console.WriteLine(students.ContainsValue(6.70)); //False

            Console.WriteLine(students.Count); //брой на записи в речника

            Console.WriteLine(students["Pesho"]); //5.60
            students["Niki"] = 5.90;
            //Pesho -> 5.60
            //Niki -> 5.90
            Console.WriteLine(students["Niki"]); //5.90

            students["Petar"] = 4.70;
            //Pesho -> 5.60
            //Niki -> 5.90
            //Petar -> 4.70

            students.Clear(); //премахне всички записи в речника
        }
    }
}