Variables and Constants

Our next example is to write some programs that does mathematical computations. But before that can be effectively we have to talk about variables and constants.

What is a variable?

A variable is a storage location in your computer memory where data can be stored and retrieved.

A variable name can be any combination of letters, letters and numbers, etc, but cannot have spaces e.g. fashion90, car, la2k, etc. Do not begin variable name with number. Like 5kay, 100weo, are all wrong variable names. And remember that a variable name does not allow spaces instead use underscore sign (_).

The major types of variable types used in C# are:

1.   Int: These includes numbers without decimal part.

2.   Double: these includes numbers with decimal part.

3.   Float: same with double.

4.   String: used to display strings of characters.

5.   Char: same as string.

The various types in C# are enormous but we are going to discuss the few above.

What are constants?

Unlike variables constants are data storage location. As the name implies constants do not change.

Now let us demonstrate the above concepts with programs that multiply two numbers.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace myfirstprogram

{

    class Program

    {

        static void Main(string[] args)

        {

           

            double num1, num2, result;

            Console.WriteLine("Enter the value for num1");

            num1 = Convert.ToDouble(Console.ReadLine()); // assigning value to num1

            Console.WriteLine("Enter the value for num2");

            num2 = Convert.ToDouble(Console.ReadLine());// assigning value to num1

            result = num1 * num2; //mutiply two numbers

            Console.WriteLine("Result=" + result);

        }

    }

}

The program above shows the use of variables. You will notice that the user can input any value for num1 and num2. The result will always be different.

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace myfirstprogram

{

    class Program

    {

        static void Main(string[] args)

        {

            double num1, num2, result;

           

            num1 = 3; // assigning value to num1

           

            num2 = 4;// assigning value to num1

            result = num1 * num2; //mutiply two numbers

            Console.WriteLine("Result=" + result);

        }

    }

}

The program shows the use of constant. Like I said earlier on that constant do not change. You will notice that when you run the program several time, it will always display the same result (12);

Try this:

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

namespace myfirstprogram

{

    class Program

    {

        static void Main(string[] args)

        {

            string a;

            Console.WriteLine("what is your name?");

            a=Convert.ToString(Console.ReadLine());

            Console.WriteLine("Hello" + a);

           

           

        }

    }

}

Study the program above and tell me what it does. You are free to copy the code into your C# environment.