Week 1 - Expressions

Table of contents

Expressions
Variables
Strings
Type Conversion
User Input and Output
- Console Input
- Console Output

In this topic, we will learn about the basic building blocks of C# programs, which are types, expressions, and variables.

Expressions

An expression is a combination of values, variables, operators, and method calls that are evaluated to produce a single value.

// This is an expression
int x = 5 + 3;

// Evaluate the type of the expression
Console.WriteLine(x.GetType());
// Output: System.Int32

Variables

A variable is a named storage location that can hold a value of a particular type.

// Declare a variable
int x;

// Assign a value to the variable
x = 5;

// Display the value of the variable
Console.WriteLine(x);

Common variable types:

Type	Description
`int`	A 32-bit signed integer
`double`	A double-precision floating point number
`char`	A single 16-bit Unicode character
`string`	A sequence of Unicode characters
`bool`	A Boolean value

Strings

A string is a sequence of Unicode characters.

// Declare a string
string name = "Dan";

// Concatenate strings
string greeting = "Hello " + name;

// Interpolate strings
string greeting = $"Hello {name}";

// String formatting
string greeting = string.Format("Hello {0}", name);

// String methods

// 1. Length: Returns the length of the string
Console.WriteLine(name.Length);

// 2. ToUpper: Returns the string in uppercase
Console.WriteLine(name.ToUpper());

// 3. ToLower: Returns the string in lowercase
Console.WriteLine(name.ToLower());

// 4. Contains: Returns true if the string contains the specified value
Console.WriteLine(name.Contains("o"));

// 5. StartsWith: Returns true if the string starts with the specified value
Console.WriteLine(name.StartsWith("J"));

// 6. EndsWith: Returns true if the string ends with the specified value
Console.WriteLine(name.EndsWith("n"));

// 7. IndexOf: Returns the index of the first occurrence of the specified value
Console.WriteLine(name.IndexOf("o"));

// 8. LastIndexOf: Returns the index of the last occurrence of the specified value
Console.WriteLine(name.Substring(1, 2));

For more information on strings, see String Class.

Type Conversion

Type conversion is the process of converting a value from one type to another. There are two types of type conversion:

Implicit conversion: No data is lost in this conversion. The conversion is done automatically by the compiler.
Explicit conversion: Data may be lost in this conversion. The conversion must be explicitly requested by the programmer using a cast operator.

Example of implicit conversion:

int x = 5;
double y = x;

Example of explicit conversion:

double x = 5.5;
int y = (int)x;

// By doing this, we lose the decimal part of the number

User Input and Output

Console Input

To read input from the console, we use the Console.ReadLine() method. This method returns a string.

string name = Console.ReadLine();

Console Output

To write output to the console, we use the Console.WriteLine() method.

Console.WriteLine("Hello World!");