C# Tutorial for Frontend Developer

1.Basic

Hello World

Console output -> console.log

Console.WriteLine("Hello World!");

Variable declaration and value assignment

string aFriend = "Bill"; 
Console.WriteLine(aFriend);

aFriend = "Maira"; 
Console.WriteLine(aFriend);

String joining with '+' (not recommended in project)

// work, but bad
Console.WriteLine("Hello " + aFriend);
// work as good, String interpolation
Console.WriteLine($"Hello {aFriend}");

string firstFriend = "Maria"; 
string secondFriend = "Sage"; 
Console.WriteLine($"My friends are {firstFriend} and {secondFriend}");
// work with properties
Console.WriteLine($"The name {firstFriend} has {firstFriend.Length} letters."); Console.WriteLine($"The name {secondFriend} has {secondFriend.Length} letters.");

Trim, TrimStart, TrimEnd

string greeting = " Hello World! "; 
Console.WriteLine($"[{greeting}]"); 

string trimmedGreeting = greeting.TrimStart(); 
Console.WriteLine($"[{trimmedGreeting}]"); 

trimmedGreeting = greeting.TrimEnd(); 
Console.WriteLine($"[{trimmedGreeting}]"); 

trimmedGreeting = greeting.Trim(); 
Console.WriteLine($"[{trimmedGreeting}]");

Replace

string sayHello = "Hello World!"; 
Console.WriteLine(sayHello); 
sayHello = sayHello.Replace("Hello", "Greetings"); 
Console.WriteLine(sayHello);

ToUpper, ToLower

Console.WriteLine(sayHello.ToUpper()); 
Console.WriteLine(sayHello.ToLower());

Contains

string songLyrics = "You say goodbye, and I say hello"; Console.WriteLine(songLyrics.Contains("goodbye")); Console.WriteLine(songLyrics.Contains("greetings"));

StartsWith and EndsWith

string songLyrics = "You say goodbye, and I say hello"; Console.WriteLine(songLyrics.StartsWith("You")); Console.WriteLine(songLyrics.StartsWith("goodbye")); Console.WriteLine(songLyrics.EndsWith("hello")); Console.WriteLine(songLyrics.EndsWith("goodbye"));

Numbers in C#

int a = 18; 
int b = 6; 
int c = a + b; 
Console.WriteLine(c);

• int as integer
• - for subtraction
• * for multiplication
• / for division

Subtraction

int c = a - b;

Multiplication

int c = a * b;

Division

int c = a / b;

Multiplication and division take precedence over addition and subtraction.

int a = 5;
int b = 4;
int c = 2;
int d = a + b * c;
Console.WriteLine(d);

You can force a different order of operation by adding parentheses around the operation or operations you want performed first:

int a = 5;
int b = 4;
int c = 2;
int d = (a + b) * c;
Console.WriteLine(d);

Replace the fourth line above with something like this:

int d = (a + b) - 6 * c + (12 * 4) / 3 + 12;

Integer division always produces an integer result, even when you'd expect the result to include a decimal or fractional portion.

int a = 7;
int b = 4;
int c = 3;
int d = (a + b) / c;
Console.WriteLine(d);

That last sample showed you that integer division truncates the result. You can get the remainder by using the remainder operator, the % character:

int a = 7;
int b = 4;
int c = 3;
int d = (a + b) / c;
int e = (a + b) % c;
Console.WriteLine($"quotient: {d}");
Console.WriteLine($"remainder: {e}");

int max = int.MaxValue;
int min = int.MinValue;
Console.WriteLine($"The range of integers is {min} to {max}");

If a calculation produces a value that exceeds those limits, you have an underflow or overflow condition.

int what = max + 3;
Console.WriteLine($"An example of overflow: {what}");

Work with the double type

The double numeric type represents a double-precision floating point number. Those terms may be new to you. A floating point number is useful to represent non-integral numbers that may be very large or small in magnitude. Double-precision is a relative term that describes the numbers of binary digits used to store the value. Double precision number have twice the number of binary digits as single-precision. On modern computers, it is more common to use double precision than single precision numbers. Single precision numbers are declared using the float keyword. Let's explore. Try the following code in the interactive window and see the result:

double a = 5;
double b = 4;
double c = 2;
double d = (a + b) / c;
Console.WriteLine(d);

Notice that the answer includes the decimal portion of the quotient. Try a slightly more complicated expression with doubles:

double a = 19;
double b = 23;
double c = 8;
double d = (a + b) / c;
Console.WriteLine(d);

double max = double.MaxValue;
double min = double.MinValue;
Console.WriteLine($"The range of double is {min} to {max}");

These values are printed out in scientific notation. The number to the left of the E is the significand. The number to the right is the exponent, as a power of 10.Just like decimal numbers in math, doubles in C# can have rounding errors. Try this code:

double third = 1.0 / 3.0;
Console.WriteLine(third);

Work with decimal types

You've seen the basic numeric types in C#: integers and doubles. There's one other type to learn: the decimal type. The decimal type has a smaller range but greater precision than double. Let's take a look:

decimal min = decimal.MinValue;
decimal max = decimal.MaxValue;
Console.WriteLine($"The range of the decimal type is {min} to {max}");

Notice that the range is smaller than the double type. You can see the greater precision with the decimal type by trying the following code:

double a = 1.0;
double b = 3.0;
Console.WriteLine(a / b);

decimal c = 1.0M;
decimal d = 3.0M;
Console.WriteLine(c / d);

The M suffix on the numbers is how you indicate that a constant should use the decimal type.Notice that the math using the decimal type has more digits to the right of the decimal point.
The M suffix on the numbers is how you indicate that a constant should use the decimal type. Otherwise, the compiler assumes the double type.

ChallengeNow that you've seen the different numeric types, write code that calculates the area of a circle whose radius is 2.50 centimeters. Remember that the area of a circle is the radius squared multiplied by PI. One hint: .NET contains a constant for PI, Math.PI that you can use for that value. Math.PI, like all constants declared in the System.Math namespace, is a double value. For that reason, you should use double instead of decimal values for this challenge.You should get an answer between 19 and 20.

double radius = 2.50;
double area = Math.PI * radius * radius;
Console.WriteLine(area);

Logic with Branch and Loop statements

int a = 5;
int b = 6;
if (a + b > 10)
    Console.WriteLine("The answer is greater than 10.");

Modify the declaration of b so that the sum is less than 10:

int b = 3;

Select the Run button again. Because the answer is less than 10, nothing is printed. The condition you're testing is false. You don't have any code to execute because you've only written one of the possible branches for an if statement: the true branch.

Tip
As you explore C# (or any programming language), you'll make mistakes when you write code. The compiler will find those errors and report them to you. When the output contains error messages, look closely at the example code, and the code in the interactive window to see what to fix. That exercise will help you learn the structure of C# code.

This first sample shows the power of if and boolean types. A boolean is a variable that can have one of two values: true or false. C# defines a special type, bool for boolean variables. The if statement checks the value of a bool. When the value is true, the statement following the if executes. Otherwise, it's skipped.This process of checking conditions and executing statements based on those conditions is powerful. Let's explore more.

To execute different code in both the true and false branches, you create an else branch that executes when the condition is false. Try this:

int a = 5;
int b = 3;
if (a + b > 10)
    Console.WriteLine("The answer is greater than 10");
else
    Console.WriteLine("The answer is not greater than 10");

int a = 5;
int b = 3;
if (a + b > 10)
{
    Console.WriteLine("The answer is greater than 10");
}
else
{
    Console.WriteLine("The answer is not greater than 10");
}

int a = 5;
int b = 3;
int c = 4;
if ((a + b + c > 10) && (a == b))
{
    Console.WriteLine("The answer is greater than 10");
    Console.WriteLine("And the first number is equal to the second");
}
else
{
    Console.WriteLine("The answer is not greater than 10");
    Console.WriteLine("Or the first number is not equal to the second");
}

The && represents "and". It means both conditions must be true to execute the statement in the true branch. These examples also show that you can have multiple statements in each conditional branch, provided you enclose them in { and }.

int a = 5;
int b = 3;
int c = 4;
if ((a + b + c > 10) || (a == b))
{
    Console.WriteLine("The answer is greater than 10");
    Console.WriteLine("Or the first number is equal to the second");
}
else
{
    Console.WriteLine("The answer is not greater than 10");
    Console.WriteLine("And the first number is not equal to the second");
}

Modify the values of a, b, and c and switch between && and || to explore. You'll gain more understanding of how the && and || operators work.

Use loops to repeat operations

int counter = 0;
while (counter < 10)
{
  Console.WriteLine($"Hello World! The counter is {counter}");
  counter++;
}

The while statement checks a condition and executes the statement following the while. It will repeat checking the condition and executing those statements until the condition is false.There's one other new operator in this example. The ++ after the counter variable is the increment operator. It adds 1 to the value of counter, and stores that value in the counter variable.

Make sure that the while loop condition does switch to false as you execute the code. Otherwise, you create an infinite loop where your program never ends. Let's not demonstrate that, because the engine that runs your code will time out and you'll see no output from your program.

The while loop tests the condition before executing the code following the while. The do ... while loop executes the code first, and then checks the condition. It looks like this:

int counter = 0;
do
{
  Console.WriteLine($"Hello World! The counter is {counter}");
  counter++;
} while (counter < 10);

Work with the for loop

for(int counter = 0; counter < 10; counter++)
{
  Console.WriteLine($"Hello World! The counter is {counter}");
}

The for statement has three parts that control how it works.
The first part is the for initializer: int counter = 0; declares that counter is the loop variable, and sets its initial value to 0.
The middle part is the for condition: counter < 10 declares that this for loop continues to execute as long as the value of counter is less than 10.
The final part is the for iterator: counter++ specifies how to modify the loop variable after executing the block following the for statement. Here, it specifies that counter should be incremented by 1 each time the block executes.

Experiment with these yourself. Try each of the following:

• Change the initializer to start at a different value.
• Change the condition to stop at a different value.

Created nested loops

for (int row = 1; row < 11; row++)
{
  Console.WriteLine($"The row is {row}");
}

for (char column = 'a'; column < 'k'; column++)
{
  Console.WriteLine($"The column is {column}");
}

for (int row = 1; row < 11; row++)
{
  for (char column = 'a'; column < 'k'; column++)
  {
    Console.WriteLine($"The cell is ({row}, {column})");
  }
}

Now that you've seen the if statement and the looping constructs in the C# language, see if you can write C# code to find the sum of all integers 1 through 20 that are divisible by 3. Here are a few hints:

• The % operator gives you the remainder of a division operation.
• The if statement gives you the condition to see if a number should be part of the sum.
• The for loop can help you repeat a series of steps for all the numbers 1 through 20.

Try it yourself. Then check how you did. As a hint, you should get 63 for an answer.

int sum = 0;
for (int number = 1; number < 21; number++)
{
  if (number % 3 == 0)
  {
    sum = sum + number;
  }
}
Console.WriteLine($"The sum is {sum}");

data collections using the generic list type

var names = new List<string> { "<name>", "Ana", "Felipe" };
foreach (var name in names)
{
  Console.WriteLine($"Hello {name.ToUpper()}!");
}

Modify list contents

Console.WriteLine();
names.Add("Maria");
names.Add("Bill");
names.Remove("Ana");
foreach (var name in names)
{
  Console.WriteLine($"Hello {name.ToUpper()}!");
}

Console.WriteLine($"My name is {names[0]}.");
Console.WriteLine($"I've added {names[2]} and {names[3]} to the list.");

Console.WriteLine($"The list has {names.Count} people in it");

IndexOf, If the item isn't in the list, IndexOf returns -1.

var index = names.IndexOf("Felipe");
if (index != -1)
  Console.WriteLine($"The name {names[index]} is at index {index}");

var notFound = names.IndexOf("Not Found");
  Console.WriteLine($"When an item is not found, IndexOf returns {notFound}");

Sort

names.Sort();
foreach (var name in names)
{
  Console.WriteLine($"Hello {name.ToUpper()}!");
}

Lists of other types

var fibonacciNumbers = new List<int> {1, 1};

var previous = fibonacciNumbers[fibonacciNumbers.Count - 1];
var previous2 = fibonacciNumbers[fibonacciNumbers.Count - 2];

fibonacciNumbers.Add(previous + previous2);

foreach(var item in fibonacciNumbers)
    Console.WriteLine(item);

See if you can put together some of the concepts from this and earlier lessons. Expand on what you've built so far with Fibonacci Numbers. Try and write the code to generate the first 20 numbers in the sequence. (As a hint, the 20th Fibonacci number is 6765.)

var fibonacciNumbers = new List<int> {1, 1};

while (fibonacciNumbers.Count < 20)
{
    var previous = fibonacciNumbers[fibonacciNumbers.Count - 1];
    var previous2 = fibonacciNumbers[fibonacciNumbers.Count - 2];

    fibonacciNumbers.Add(previous + previous2);
}
foreach(var item in fibonacciNumbers)
    Console.WriteLine(item);

---

2.Explore object oriented programming with classes and objects

Explore object oriented programming with classes and objects

Empty program

using System;

namespace classes
{
    class Program
    {
        static void Main(string[] args)
        {
            Console.WriteLine("Hello World!");
        }
    }
}

In this tutorial, you're going to create new types that represent a bank account. Typically developers define each class in a different text file. That makes it easier to manage as a program grows in size. Create a new file named BankAccount.cs in the classes directory.

This file will contain the definition of a bank account. Object Oriented programming organizes code by creating types in the form of classes. These classes contain the code that represents a specific entity. The BankAccount class represents a bank account. The code implements specific operations through methods and properties. In this tutorial, the bank account supports this behavior:

• It has a 10-digit number that uniquely identifies the bank account.
• It has a string that stores the name or names of the owners.
• The balance can be retrieved.
• It accepts deposits.
• It accepts withdrawals.
• The initial balance must be positive.
• Withdrawals cannot result in a negative balance.

Define the bank account type

You can start by creating the basics of a class that defines that behavior. Create a new file using the File:New command. Name it BankAccount.cs. Add the following code to your BankAccount.cs file:

using System;

namespace classes
{
    public class BankAccount
    {
        public string Number { get; }
        public string Owner { get; set; }
        public decimal Balance { get; }

        public void MakeDeposit(decimal amount, DateTime date, string note)
        {
        }

        public void MakeWithdrawal(decimal amount, DateTime date, string note)
        {
        }
    }
}

Before going on, let's take a look at what you've built. The namespace declaration provides a way to logically organize your code. This tutorial is relatively small, so you'll put all the code in one namespace.

public class BankAccount defines the class, or type, you are creating. Everything inside the { and } that follows the class declaration defines the state and behavior of the class. There are five members of the BankAccount class. The first three are properties. Properties are data elements and can have code that enforces validation or other rules. The last two are methods. Methods are blocks of code that perform a single function. Reading the names of each of the members should provide enough information for you or another developer to understand what the class does.

Open a new account

public BankAccount(string name, decimal initialBalance)
{
    this.Owner = name;
    this.Balance = initialBalance;
}

var account = new BankAccount("<name>", 1000);
Console.WriteLine($"Account {account.Number} was created for {account.Owner} with {account.Balance} initial balance.");

private static int accountNumberSeed = 1234567890;