C#

• Introduction
• Getting Output
• Datatype
• Variable Declaration
• Operator
• string concatenation
• Converting Datatype
• Getting input from user
• Working on Angles
• Escape Sequence
• Conditional Statements
• If statement
• Switch statement
• Types of Error
• Exception Handling
• Loop
• While Loop
• For Loop
• Do While Loop
• Array
• Foreach Loop
• Multi dimensional array
• Nested Loop
• Jump Statment
• String Handling Function
• Methods or Functions
• Passing Parameter
• Method Overloading
• Void Function
• Returning Function
• Class
• Creating New Instance
• Static Keyword
• Constructor
• Constructor Overloading
• Destructor
• Inheritance
• Multi Level Inheritance
• Multiple Inheritance
• Sealed Class
• Partial Class
• Upcasting
• Abstract Class
• Interface
• Ref,Out,In Parameters
• Field Vs Property
• Struct
• DateTime
• Enum
• Namespace
• Dynamic Link Library(DLL)
• Collections
• File Handling
• Excel handling

Excel File Handling

We can handle Excel files using our C# Code. Excel files are different from other files because it is having multi dimensional contents(Rows and Columns). Before entering code part we need to follow some preliminary steps to handle excel files where adding the Excel file reference(Same like adding DLL file) is the first step.

STEPS TO FOLLOW:
1. Open Visual Studio, Choose Console App(.NET Framework) template.
2. You will find Solution Explorer window in the Right Hand side, if not go to top menu choose View - Solution Explorer.
3. Inside solution explorer there is an option called References. Right click that References and click Add reference.
4. Once after 3rd step Reference Manager window will open. In the Left hand side choose COM.
5. In the top right corner, there will be Search box. Type Excel there. Now System will filter library files related to Excel.
6. Choose Microsoft Excel *version* Object Library(Your system must be installed with Excel, Only then you will find this library) and click OK in bottom right.
7. We are all set, Its time to handle Excel files using our C# Code.

CODE

EG 1 . Reading, Writing values in Excel file using C# Code.

//We can give name to our Namespaces(Below we named as Excel). We referred Excel namespaces below so that no need to call it each time.
using Excel = Microsoft.Office.Interop.Excel;

namespace projectName{
    class Program {
        static void Main() {
            //------ 1. Writing Content in Excel sheet ------
            Excel.Application xlapp = System.Runtime.InteropServices.Marshal.GetActiveObject("Excel.Application") as Excel.Application;
            Excel.Workbook wb = xlapp.ActiveWorkbook;
            Excel.Worksheet ws = wb.ActiveSheet;
            ws.Cells[100, 1] = "CodersCapsule";

            //------ 2. Reading Excel sheet ------
            Excel.Application xlapp = System.Runtime.InteropServices.Marshal.GetActiveObject("Excel.Application") as Excel.Application;
            Excel.Workbook wb = xlapp.ActiveWorkbook;
            Excel.Worksheet ws = wb.Sheets[3];
            string valueInCell = ws.Cells[1, 1].value;
            Console.WriteLine(valueInCell);
        }
    }
}


CODE EXPLANATION
Before entering explantaion part, We need to open excel application, create new excel project then we need to compile the above program in order for above program to work.

1. In order to handle Excel sheet we need use the interfaces present inside Microsoft.Office.Interop.Excel namespace. Hence we referred those namespaces and named it as Excel in the top. Now no need to call those namespaces each time, we can simply use Excel name to access those. First we need to use Application interface to tell the system which excel application to handle. We created an Application instance called xlapp. Now whatever current active excel application will be taken for modifications. Inside Excel we are having something called Workbook and WorkSheet. Workbook is the current project we opened in Excel Application. Worksheet is the current active sheet we opened in Excel Application. In order to access Cells inside Worksheet we need to use the Worksheet's instance name and Cells property. In the above 1st code, we are telling the system to take the current opened Project and current Active work sheet for writing. We instructing the compiler to write CodersCapsule text in the 100th row and 1st Column cell of current active sheet.

2. The function of Application and Workbook are same as that of the function of 1st code. Here in Excel's Worksheet instead of giving current active sheet we've instructed the compiler to take 3rd sheet from the current project. Assume in 3rd sheet of current opened project in 1st row and 1st column cell we are having CoderCapsule text. Now that value will be taken and stored inside local field called valueInCell and printed out in console.

NOTE
In the above code, we used System.Runtime.InteropServices to tell the system to take current active excel application. Instead of writing System.Runtime.InteropServices which is a namespace, we can simple refer them in the top by writing using System.Runtime.InteropServices; so that no need to call it each time.

Exercises
1. Get number of rows value from user in console, Print Right Angle Triangle shape using * in Excel file(1 star(*) per each cell).

(Click Here, For more exercises)