C# Variable Declaration and Initialization
This example demonstrates variable declaration and initialization in C# using common data types such as int, float, double, decimal, char, string, and bool. It also demonstrates three ways to display variable values: concatenation, string interpolation, and String.Format.
10 AM Class
What you'll cover
Learning objectives
- Understand variable declaration and initialization in C#
- Identify common C# data types
- Initialize variables with appropriate literal suffixes
- Display variable values using concatenation
- Display variable values using string interpolation
- Display variable values using String.Format
- Understand positional format placeholders such as {0}, {1}, and {2}
Prerequisites
Related topics
Concept breakdown
Variable Declaration and Initialization
A variable stores a value of a particular data type. In C#, a variable can be declared with its data type and initialized with a value in the same statement, as demonstrated in the example.
int
The int variable a is initialized with the integer value 100.
float
The float variable b is initialized with 12.23f. The f suffix indicates a float literal.
double
The double variable c is initialized with 23.45.
decimal
The decimal variable d is initialized with 34.56m. The m suffix indicates a decimal literal.
char
The char variable e is initialized with the character 'A'.
string
The string variable f is initialized with the text Hello, World!.
bool
The bool variable g is initialized with the Boolean value true.
String Concatenation
The example uses the + operator to combine text with variable values, such as "a value is :" + a.
String Interpolation
The example uses the $ prefix and expressions inside braces, such as $"a value is : {a}".
String.Format
The example uses placeholders such as {0} and passes the corresponding variables as arguments to Console.WriteLine().
C# Variable Declaration and Initialization Example
> "a value is :100"> "b value is :12.23"> "c value is :23.45"> "d value is :34.56"> "e value is :A"> "f value is :Hello, World!"> "g value is :True"> ""> "a value is : 100"> "b value is : 12.23"> "c value is : 23.45"> "d value is : 34.56"> "e value is : A"> "f value is : Hello, World!"> "g value is : True"> ""> "a value is : 100"> "b value is : 12.23"> "c value is : 23.45"> "d value is : 34.56"> "e value is : A"> "f value is : Hello, World!"> "g value is : True"> ""> "a value is : 100"> "b value is : 12.23"> "c value is : 23.45"> "d value is : 34.56"> "e value is : A"> "f value is : Hello, World!"> "g value is : True"
Step by step
- 1
Import Namespaces
The program imports System, System.Collections.Generic, and System.Text.
- 2
Declare the Namespace
The Class3 class is placed inside the ConApp1 namespace.
- 3
Declare and Initialize Variables
Seven variables are declared and initialized using int, float, double, decimal, char, string, and bool.
- 4
Display Using Concatenation
The + operator combines each descriptive string with its corresponding variable value.
- 5
Display Using String Interpolation
The $ prefix enables expressions such as {a} to be embedded directly inside the string.
- 6
Display Using String.Format
Numbered placeholders such as {0} are used and the corresponding variable is supplied as an argument.
- 7
Display Multiple Values with String.Format
The final Console.WriteLine uses placeholders from {0} through {6} and supplies all seven variables in the same order.
Key takeaways
Key points
- Variables are declared with a data type and variable name.
- Variables can be initialized at the time of declaration.
- The example uses int, float, double, decimal, char, string, and bool.
- The float literal uses the f suffix.
- The decimal literal uses the m suffix.
- String concatenation uses the + operator.
- String interpolation uses the $ prefix and braces.
- String.Format-style formatting uses numbered placeholders.
- The final statement maps {0} to a, {1} to b, through {6} to g.
Advantages
- Clear and simple variable declarations.
- Strong typing makes the intended data type explicit.
- String interpolation provides readable formatting.
- String.Format supports numbered placeholders and multiple values.
- The example demonstrates several common ways to display data.
Disadvantages
- Concatenation can become harder to read when many values are combined.
- String.Format with many numbered placeholders can be less readable because values must be matched by position.
- Using many variables without meaningful names can reduce code readability.
Displaying Employee Information
An application may declare variables such as employee ID, salary, department, employee name, and active status, then display those values using concatenation, interpolation, or formatted strings.
Frequently asked questions
Variable declaration specifies the data type and name of a variable.
Variable initialization assigns an initial value to a variable.
int, float, double, decimal, char, string, and bool.
The f suffix identifies the numeric literal as a float literal.
The m suffix identifies the numeric literal as a decimal literal.
String concatenation combines strings and values, using the + operator in this example.
String interpolation allows expressions to be embedded inside a string using the $ prefix and braces.
It uses numbered placeholders such as {0} and supplies the corresponding variables as arguments.
The bool variable g is initialized with true.
Quick MCQ practice
1. Which data type is used for variable a?
2. Which suffix is used for the float literal 12.23?
3. Which suffix is used for the decimal literal 34.56?
4. Which variable stores the character A?
5. Which variable stores Hello, World!?
6. Which variable is of type bool?
7. Which operator is used for concatenation in the example?
8. Which syntax represents string interpolation?
Practice on your own
Coding exercise
C# Variable Declaration and Output Formatting
Declare variables using int, float, double, decimal, char, string, and bool. Initialize them with suitable values and display them using concatenation, string interpolation, and String.Format.
Assignment
- Declare variables using int, float, double, decimal, char, string, and bool.
- Initialize each variable with a suitable value.
- Display all values using string concatenation.
- Display all values using string interpolation.
- Display all values using String.Format-style placeholders.
- Display multiple variables in a single formatted Console.WriteLine statement.
Tags
References
