Variables and Data Types

In the last lesson, you saw a variable in action when we used string name = Console.ReadLine();. Now let us talk about what variables really are and the different types of data you can work with.

Think of a variable as a labeled box. You put something inside the box, give it a name, and then you can refer to that box whenever you need what is inside. In programming, variables store data.

Declaring Variables

In C#, you declare a variable by specifying its type and giving it a name. Here is the pattern:

type name = value;

For example:

int age = 25;
string name = "Amina";
double height = 5.6;
bool isStudent = true;

See how each variable has a different type? That is because C# is a strongly-typed language. This means you have to tell it what kind of data each variable will hold. It might seem annoying at first, but trust me, it saves you from a lot of bugs down the road.

Common Data Types

Here are the data types you will use most often:

• int — whole numbers like 1, 42, -7, 100
• double — decimal numbers like 3.14, -0.5, 100.0
• float — also decimal numbers, but uses less memory (you need to add an 'f' suffix: 3.14f)
• decimal — high-precision decimals, great for money calculations
• string — text like "Hello", "Kano", "25" (yes, numbers in quotes are strings)
• bool — either true or false
• char — a single character like 'A', 'z', '9'

Naming Rules

You cannot just name variables whatever you want. There are a few rules:

• Names must start with a letter or underscore
• They can contain letters, numbers, and underscores
• You cannot use C# keywords like int, string, class as variable names
• C# is case-sensitive — age and Age are two different variables

The convention in C# is to use camelCase for variables (first word lowercase, subsequent words capitalized) and PascalCase for class names (each word capitalized).

int studentCount = 30;       // camelCase
string firstName = "Bilal";  // camelCase
class StudentRecord { }      // PascalCase

Using Variables

Once you have declared a variable, you can use it in your code. You can print it, do math with it, combine it with other variables, and more:

string name = "Fatima";
int age = 22;

Console.WriteLine("Name: " + name);
Console.WriteLine("Age: " + age);
Console.WriteLine("Next year, " + name + " will be " + (age + 1));

Notice how we use the + operator to combine strings with other values. This is called string concatenation. It works, but there is a better way to do it — string interpolation. We will cover that soon.