Learn C# in 7 Days : Day 1

Learning C# for beginners can be little difficult in the first place. But it isn’t that difficult.

When starting to learn C# you should start with the basics and not get into the deep rabbit hole of it.

This is Day 1 of Learn C# in 7 Days.

Let’s begin…

Things you’ll need to get started

• PC
• Visual Studio Express or Community Edition
• Interest to learn C#

Hello World Program

Every programming language is made up by using words and letters known as Keywords.

While programming we use letters and words to form expressions and statements and then those statements can be used within isolated function bodies called as methods.

 class ExampleHelloWorld
{
static void Main()
{
Console.WriteLine("Hello World");
}
}

In the above given example, class, static, void are keywords and Main() is a method defined by the end user which acts as the entry point for the HelloWorld program.

C# is an object-oriented programming language. We won’t be going into the topic of Classes and Objects as of now.

Let’s dissect the above give example.

Console is a C# class coming from the System namespace.

Object-oriented programming is about creating objects from classes and then using variables and calling methods of those objects.

Similarly, in the above code example, Console is a class which has a method called WriteLine which prints a value or any data on the console.

Now, How and what will the WriteLine method print on the console? It won’t do anything on its own.

We need to instruct the WriteLine method what to print on the screen and we can do that by passing data to the method known as arguments.

Console.WriteLine("Hello World");

in the above line of code we are passing a string i.e. “Hello World” to the WriteLine method. It’s the job of the WriteLine method to print the given data via arguments on the console screen.

Comments in CSharp

Code without comments and documentation is bad code.

Comments are lines of text which gives information about the flow of the program and what does a method do when it’s called.

There are three types of comments:

• Single line comments
• Multi-Line comments
• XML Documentation comments

Single-Line Comments

// this is variable with int data type
int myAge = 28;

Multi-Line Comments

/* This is a multi-line comment
You can write whatever you want
*/

XML Documentation Comments

 /// <summary>
/// This is the Main Method. It is an entry point for our application
/// </summary>
static void Main()
{
string firstName = "Abhishek";
string lastName = " Luv";
string fullName = firstName + lastName;
Console.WriteLine(fullName);
}

XML documentation comments are used to write documentations for classes and methods in C#.

These XML comments are then used by Visual Studio to provide us information using Intellisense.

To write an XML comment just press / 3 times on any class or method.

Data Types in CSharp

Every program needs memory and space to store data before it performs any operations and actions on the data.

Every value has a data type associated with it.

For example:

• A word like Abhishek will be of type string in C#
• A numeric value like 12345 will be of type int in C#
• A true or false value will be of type bool in C#
• A numeric value like 233.33 will be of type float in C# and so on…

Commonly used Data Types in CSharp

• int : for numeric values
• long : for larger numeric values
• float : single-precision
• double : double-precision
• decimal : for very very very large numeric values
• string : for storing words and text
• bool : for storing true or false values

Declaring Variables using Data Types

int example:

data-type variable-name = variable-value;
int valueForA = 1200;

string example:

string myName = "Abhishek Luv";

bool example:

bool IsAvailable = true;

Arithmetic Operators in CSharp

• (+) : For addition
• (-) : for subtraction
• (*) : multiplication
• / : division
• % : modulus
• ++ : increment
• – : decrement

These are the basic arithmetic operators used in C#. Let’s look at some sample code.

Relational Operators in CSharp

• (>) : Greater than
• (<) : Less than
• (>=) : Greater than or equal to
• (<=) : Less than or equal to
• (!=) : Not equal to
• (==) : Equal to

Adding Number using in CSharp

 static void Main()
{
int a = 10; int b = 20;
int sum;
// here we have used + operator for addition
sum = a + b; Console.WriteLine(sum);
}

Joining two string values using + Operator

We can use the same + operator to join two string values in C#.

 static void Main()
{
string firstName = "Abhishek";
string lastName = " Luv";
// here we have used + operator for joining two string values
string fullName = firstName + lastName;
Console.WriteLine(fullName);
}

Playing with If Else If Statement

 static void Main()
{
PlayingWithIf(20, 20);
}
static void PlayingWithIf(int x, int y)
{
if (x < y)
{
Console.WriteLine("x is less than y");
}
else if (x > y)
{
Console.WriteLine("x is greater than y");
}
else if (x == y)
{
Console.WriteLine("x is equal to y");
}
else
{
Console.WriteLine("invalid numbers");
}
}

In this example, we have a static void method called PlayingWithIf which uses If Else If statements with relational operators to print the desired output on the console screen. Don’t worry about what is static and void. We’ll come to that.

if(x < y) // if x is less than y then print "x is less than y"
else if(x > y) // if x is greater than y then print "x is greater than y"
else if(x == y) // if x is equal to y then print "x is equal to y"
else....

Notice that the PlayingWithIf method takes in two arguments i.e. whenever the PlayingWithIf method is called we will have to provide two arguments or two values to the method.

 static void Main()
{
PlayingWithIf(20, 20);
}

Here, we are calling the PlayingWithIf method in our Main method with two arguments (20,20).

It’s always better to write a standalone method than stuffing the entire Main method with code.

For Loop Statements

A For loop statement is used for looping to perform actions based on the initial value and the test condition declared within a For loop.

For example Lets print numbers 10 to 0 using a for loop

 static void Main()
{
for (int i = 10; i >= 0; i--)
{
Console.WriteLine(i);
}
}

In this example, we have declared an initial variable int i with a value of 10 i.e. we are saying the For loop to set the initial value equal to 10.

i >= 0; is the condition defined within the loop. This instructs the for loop to keep running the loop until the value i is greater than or equal to 0.

i-- is the action to performed by the for loop for us.

As the loop runs with the help of i-- the value i is decremented by -1 till the condition i >= 0 is met.

While Loop

let’s look at the same example using a while loop in C#.

 static void Main()
{
int i = 10; // initial variables declared
while (i >= 0) // test condition
{
Console.WriteLine(i);
i--; // action to be performed every time the loop runs
}
}

In a While loop, we declare the initial variable and value outside the loop.

While loop starts with a test condition and then the body of the loop within curly braces {}.

Here, the condition is to keep running the loop until the value of i is greater than or equal to zero.

And the action to be performed in within the while loop i.e. i--.

Do..While loop

Do..While loop is very similar to the While loop but with only two differences.

First Difference

In a Do..While loop the statements inside the body of the loop are executed once before any conditions are met or the actions are performed by the loop.

For example:

 static void Main()
{
int i = 0;
do
{
Console.WriteLine(i);
i++;
} while (i <= 10);
}

Second Difference

Here, an initial value of i is 0. In a Do..While loop the condition is checked at the end of the loop and in a While loop at the beginning of the loop

And the actions i++ is performed within the Do loop.

Commonly used Logical Operators in CSharp

• && : logical AND
• || : logical OR

Example:

 static void Main()
{
CheckNumbers(10, 20);
}
static void CheckNumbers(int x, int y)
{
if (x >= 0 && y >= 0)
{
Console.WriteLine("both numbers positive");
}
else if (x >= 0 || y >= 0)
{
Console.WriteLine("at least one num is positive");
}
else
{
Console.WriteLine("both are negative");
}
}

In the above code example, we have a method called CheckNumbers.

The CheckNumbers method takes in two arguments to check whether the numbers are positive or negative.

if (x >= 0 && y >= 0) // 10 >= 0 && 20 >= 0 // Result will be : both numbers are positive

Condition 10 >= 0 will return true and 20 >= 0 will also return true. So, true * true is true i.e. both numbers are positive.

Similarly OR || is used to check at least one positive number and the else block executes when both the numbers are negative.

Switch Case Statement

Switch case statements are very similar to If statements. Switch case can be used with any data type.

In a switch case statement, we provide a value which it uses to compare with the cases defined within the switch statement and display appropriate results on the console.

Note: Case declared within a switch case statement has to be constant

 static void Main(string[] args)
{
PlayingWithSwitchCase("three");
}
static void PlayingWithSwitchCase(string j)
{
switch (j)
{
case "two":
Console.WriteLine("you entered four in words");
break;
case "three":
Console.WriteLine("you entered three in words");
break;
default:
Console.WriteLine("error");
break;
}
}

Arrays in CSharp

Arrays are used to store a collection of data of similar data types.

For example: If you want to declared 5 int variable how will you do it?

Like this right?

int a = 1;
int b = 2;
int c = 3;
int d = 4;
int e = 5;

Now, this is a lot of code. It’s better to use arrays to store 5 int values than using 5 different int variables.

Declaring Arrays

int[] arrayName = new int[sizeofthearray];
int[] intArray = new int[5];

Now int[5] means that this array can hold 5 values. Values or data within an array can be accessed using an index.

For example:

intArray[0], intArray[1] and so on...

Note: Index of an array starts from value 0. i.e. If you want to access the 5th value then you need to use intArray[4]

Looping over an array to display data using For Looping

 for (int i = 0; i < intArray.Length; i++)
{
Console.WriteLine(intArray[i]);
}

The for loop uses the intArray.Length of the array to define a test condition for the loop.

Looping over an array using ForEach loop

 foreach (int tempArrayValue in intArray)
{
Console.WriteLine(tempArrayValue);
}

The ForEach loop uses a tempArrayValue variable to hold the array values one by one and display it on the console screen.

Strings in CSharp

Anything within double quotes "Abhishek Luv" in C# is a string.

Declaring a string

string myName = "Abhishek Luv";

Declaring an array of string

string[] allListOfName = { "Abhishek", "Abhijeet","Akshay" };

Commonly used String functions

• ToUpper()
• ToLower()
• SubString()
• IndexOf

Looping over an array of string using foreach loop

foreach (string names in allListOfName)
{
Console.WriteLine(names);
}

Day 1 over

Stay Tuned.

Take Care!

Abhishek Luv