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Computing

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C#

Variables

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Computing - C# Variables

Declaring Variables

Variables are used when holding data in memory while a program runs. So the program can set aside the right amount of memory to hold our information, we declare our variables to be of a particular data type.

Declaring Variables Video [3.1MB Quicktime .mov 01:39]

// Declare a variable called number1 to hold a whole number
int number1;

// Declare a variable called firstName to hold some text
string firstName;

// Declare a variable called eventDate to hold a date
DateTime eventDate;

Note: Comments have been included in the code examples to help explain certain parts of the code. Comments start with // and are there to help us understand the program but are ignored by the computer.

There is a number of different data types that we will come across on a regular basis:

int

Integers (whole numbers). E.g. 5, -123, 5600204

double

Numbers with decimal parts. E.g. 6.23, -0.0054, 2.0

string

Text. E.g. "Hello World!"

bool

Boolean. True or False

DateTime

Dates, Times, Dates and Times. E.g. 16/10/2009

A variable called number1 is created to hold a whole number.

Assignment

To use a variable, we assign it a value using the assignment operator, =. The value from the right of the assignment operator is stored in the variable named on the left of the operator.

// Declare a variable called number1 to hold a whole number
int number1;

// Assign a value of 6 to the variable called number1
number1 = 6;

// Declare a variable called firstName to hold some text
string firstName;

// Assign a value of "Barry" to the variable called firstName
firstName = "Barry";

The value assigned can be the result of a calculation.

// Declare three variables to hold whole numbers
int number1;
int number2;
int total;

// Assign values to number1 and number2
number1 = 6;
number2 = 21;

// Find the sum of number1 and number2 and store it in total
total = number1 + number2;

As our programs get bigger, having readable, descriptive names for our variables will make our programs easier to follow and understand.

The literal value 6 is placed in the variable called number1.

Try It Out

Create a new Console Application and try out the following program.

class Program
{
    static void Main(string[] args)
    {
        // Declare three variables to hold whole numbers
        int number1;
        int number2;
        int total;
        
        // Assign values to number1 and number2
        number1 = 6;
        number2 = 21;

        // Find the sum of number1 and number2 and store it in total
        total = number1 + number2;
        
        // Display the values of the variables
        Console.WriteLine("The value of number1 is {0}", number1);
        Console.WriteLine("Tha value of number2 is {0}", number2);
        Console.WriteLine("The sum of number1 and number2 is {0}", total);
    }
}

The value of number1 is 6
The value of number2 is 21
The sum of number1 and number2 is 27

Assigning Values to Variables Video - Using the assignment operator with literal values and expressions. [5.1MB Quicktime .mov 02:23]

Shortcuts

Multiple variables of the same data type can be declared together in a list.

int num1, num2, num3;
string text1, text2;

Variables can be declared and assigned an initial value in a single statement.

int num1 = 17;
string text1 = "Hello";
DateTime today = DateTime.Today;

The expression is evaluated and its value placed in the variable called total.

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