10 bài tập cơ bản học lập trình C#

using System;
namespace Exercise1
{
    class Program
    {
        static void Main(string[] args)
        {
            int num1, num2, sum;
            Console.Write("Enter the first number: ");
            num1 = int.Parse(Console.ReadLine());
            Console.Write("Enter the second number: ");
            num2 = int.Parse(Console.ReadLine());
            sum = num1 + num2;
            Console.WriteLine("The sum of {0} and {1} is {2}", num1, num2, sum);
            Console.ReadLine();
        }
    }
}

using System;
namespace Exercise2
{
    class Program
    {
        static void Main(string[] args)
        {
            double radius, area;
            Console.Write("Enter the radius: ");
            radius = double.Parse(Console.ReadLine());
            area = Math.PI * radius * radius;
            Console.WriteLine("The area of the circle is {0}", area);
            Console.ReadLine();
        }
    }
}

using System;
namespace Exercise3
{
    class Program
    {
        static void Main(string[] args)
        {
            int num1, num2, num3;
            Console.Write("Enter the first number: ");
            num1 = int.Parse(Console.ReadLine());
            Console.Write("Enter the second number: ");
            num2 = int.Parse(Console.ReadLine());
            Console.Write("Enter the third number: ");
            num3 = int.Parse(Console.ReadLine());
            int max = num1;
            if (num2 > max)
            {
                max = num2;
            }
            if (num3 > max)
            {
                max = num3;
            }
            Console.WriteLine("The maximum number is {0}", max);
            Console.ReadLine();
        }
    }
}

using System;
namespace Exercise4
{
    class Program
    {
        static void Main(string[] args)
        {
            int num;
            Console.Write("Enter a number: ");
            num = int.Parse(Console.ReadLine());
            bool isPrime = true;
            for (int i = 2; i <= num / 2; i++)
            {
                if (num % i == 0)
                {
                    isPrime = false;
                    break;
                }
            }
            if (isPrime)
            {
                Console.WriteLine("{0} is a prime number", num);
            }
            else
            {
                Console.WriteLine("{0} is not a prime number", num);
            }
            Console.ReadLine();
        }
    }
}

using System;
namespace Exercise5
{
    class Program
    {
        static void Main(string[] args)
        {
            double a, b, c, delta, x1, x2;
            Console.Write("Enter the value of a: ");
            a = double.Parse(Console.ReadLine());
            Console.Write("Enter the value of b: ");
            b = double.Parse(Console.ReadLine());
            Console.Write("Enter the value of c: ");
            c = double.Parse(Console.ReadLine());
            delta = b * b - 4 * a * c;
            if (delta < 0){
                Console.WriteLine("No real roots");
            }
            else if (delta == 0) {
                x1 = -b / (2 * a);
                Console.WriteLine("The only root is {0}", x1);
            }
            else {
                x1 = (-b + Math.Sqrt(delta)) / (2 * a);
                x2 = (-b - Math.Sqrt(delta)) / (2 * a);
                Console.WriteLine("The roots are {0} and {1}", x1, x2);
                }
            Console.ReadLine();
        }
    }
}

using System;
namespace MyProgram
{
    class Program
    {
        static void Main(string[] args)
        {
            int[] arr = { 1, 2, 3, 4, 5 };
            int sum = 0;
            for (int i = 0; i < arr.Length; i++)
            {
                sum += arr[i];
            }
            Console.WriteLine("Total number is: " + sum);
        }
    }
}

using System;
namespace Exercise7
{
    class Program
    {
        static void Main(string[] args)
        {
            string str, reverse = "";
            Console.Write("Enter a string: ");
            str = Console.ReadLine();
            for (int i = str.Length - 1; i >= 0; i--)
            {
                reverse += str[i];
            }
            if (str == reverse)
            {
                Console.WriteLine("{0} is a palindrome", str);
            }
            else
            {
                Console.WriteLine("{0} is not a palindrome", str);
            }
            Console.ReadLine();
        }
    }
}

using System;
namespace Exercise8
{
    class Program
    {
        static void Main(string[] args)
        {
            for (int i = 1; i <= 9; i++)
            {
                for (int j = 1; j <= 9; j++)
                {
                    Console.Write("{0}x{1}={2}\t", j, i, i * j);
                }
                Console.WriteLine();
            }
            Console.ReadLine();
        }
    }
}

using System;
namespace Exercise9
{
    class Program
    {
        static void Main(string[] args)
        {
            for (int i = 1; i <= 100; i++)
            {
                if (i % 3 == 0 || i % 5 == 0)
                {
                    Console.WriteLine(i);
                }
            }
            Console.ReadLine();
        }
    }
}

using System;
namespace Exercise10
{
    class Program
    {
        static void Main(string[] args)
        {
            int n, n1 = 0, n2 = 1, n3;
            Console.Write("Enter the value of n: ");
            n = int.Parse(Console.ReadLine());
            if (n == 1)
            {
                Console.WriteLine("The {0}st Fibonacci number is 0", n);
            }
            else if (n == 2)
            {
                Console.WriteLine("The {0}nd Fibonacci number is 1", n);
            }
            else if (n == 3)
            {
                Console.WriteLine("The {0}rd Fibonacci number is 1", n);
            }
            else
            {
                for (int i = 3; i <= n; i++)
                {
                    n3 = n1 + n2;
                    n1 = n2;
                    n2 = n3;
                }
                Console.WriteLine("The {0}th Fibonacci number is {1}", n, n2);
            }
            Console.ReadLine();
        }
    }
}