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How to connect an application to a SQL Server using IP Adress in C#?

My problem is that I have created a SQL Server database but I access it locally, only from my own computer. What I want to do is to connect the app to a server and to save all the data there.
The code I used to connect to the SQL Server database is:
SqlConnection con = new SqlConnection(#"Data Source=(localdb)\v11.0;AttachDbFilename=C:\Users\donca\Desktop\Memo\Memo\ContNou.mdf;Integrated Security=True");
SqlCommand cmd1 = new SqlCommand("SELECT * FROM [dbo].[Cont] WHERE Nume_utilizator = #Nume_utilizator and Parola = #Parola;", con);
cmd1.Parameters.AddWithValue("#Nume_utilizator", this.Nume_utilizator.Text);
cmd1.Parameters.AddWithValue("#Parola", this.Parola.Text);
cmd1.Connection = con;
con.Open();
My question is: how can I change this to connect and access data from a SQL Server and save data there?

Just change the connection string:
"Data source=ServerName\InstanceName;"
You can use the IP address instead of the servername.
The default instance name is MSSQLSERVER.
Make sure you turn on "Remote connections" on the distant server. You can use Management studio -> Server properties -> connections -> Allow remote connections.
If it dosn't work check that the TCP/IP protocol is activated for you instance.
You can find it in SQl Server Configuration Manager.

You just have to change your connection string. That's all. For an example, if your server name is CORP and the SQL instance name is SQL2012, your connection string will be like this.
SqlConnection con = new SqlConnection(#"Data Source=CORP\SQL2012;Initial Catalog=ContNou;Integrated Security=True");
In case if you cannot find the SQL server by its name, you can use the IP too.
SqlConnection con = new SqlConnection(#"Data Source=10.4.2.208;Initial Catalog=ContNou;Integrated Security=True");

Microsoft Visual Studio SQL server connection - invalid pointer

So, I want to create a SQL database in Microsoft SQL Management Studio and connect it to Microsoft Visual Studio. I linked the database to Visual Studio and it worked. Now, I want to open that connection to test it with a button on a windows form application. Every time I try, it says "invalid pointer" but the database name is correct. I don't know what is wrong.
I still get the invalid pointer error...My instance name is DESKTOP-BJSAO6B but it doesnt seem to work...

You need provide a proper connection string like
string connectionString =
"data source=.\SQLEXPRESS;initial catalog=student;integrated security=True;";
using (SqlConnection connection =
new SqlConnection(connectionString))
{
connection.Open();
MessageBox.Show("You are connected");
}
where SQLEXPRESS - name your MSSQL instance ( may be different). More you can see here

For Ex:
string connectionString = "Data Source=Server-Name; Initial Catalog= Database-Name;Integrated Security=True"; //If you are using a local Database.
SqlConnection conn = new SqlConnection(connectionString);
conn.Open();
MessageBox.Show("You are connected");

how to update single database from two computers

I want to know how to update a database installed on two computers. I want to update only a single database. Whether I work on 1st computer or 2nd computer I want to update the database once. How can I do this?
This is my database connect method:
public static SqlConnection connect() {
String conct = #"Data Source=.\SQLEXPRESS;AttachDbFilename=E:\3000Apliance\3000Apliance\300Apliance.mdf;Integrated Security=True;User Instance=True";
SqlConnection con = new SqlConnection(conct);
con.Open();
return con;
}

Use one Computer as Server keep your database there. on other computer use sqlmanagement and connect to server computer via Ip/name 192.0.0.0/name and create a path to database.
this way you can use more then 2 computers to update database at a time. you can connect computers by peer to peer or use a switch to connect multiple computers.
your new connection string should look like this:
Data
Source = . \ SQLEXPRESS; AttachDbFilename=192.0.0.0\name\3000Apliance\3000Apliance\300Apliance.mdf; Integrated Security=True;User Instance=True";
SqlConnection con = new SqlConnection(conct);

How to backup from .mdf database that I created

I created a .mdf database file with Visual Studio 2008. I can retrieve and insert data into database but when I want to backup I receive an error.
My code:
string con = #"Data Source=.\SQLEXPRESS;AttachDbFilename=|C:\test\Data|\DB.mdf;Integrated Security=True;User Instance=True";
connect = new SqlConnection(con);
connect.Open();
SqlCommand command = new SqlCommand(#"backup database [" + System.Windows.Forms.Application.StartupPath + "\\Data\\DB.mdf] to disk ='"+str+"' with init,stats=10",connect);
command.ExecuteNonQuery();
connect.Close();
MessageBox.Show("The support of the database was successfully performed", "Back", MessageBoxButtons.OK, MessageBoxIcon.Information);
The error is:
error : invalid value for key 'attachdbfilename'.

Seems like your connection string is incorrect.
Try this one:
string con = #"Data Source=.\SQLEXPRESS;AttachDbFilename=C:\test\Data\DB.mdf;Integrated Security=True;User Instance=True";
For more options, have a look at: http://www.connectionstrings.com/sql-server-2005

This is for SQL Server 2012 and .NET 4.0.1 only.
If you have those, you should be able to use AttachDbFilename.
Anyway, if you have an .MDF for embedded database and the instance is not running, you can just copy .MDF and .LDF to back up.

just use your connection string as
SqlConnection conn = new SqlConnection(ConfigurationManager.ConnectionStrings["<your connection string name from your app.config file>"].ConnectionString);
i tried it and it worked for me.

Connecting to local SQL Server database using C#

Suppose I have created a SQL Server database called Database1.mdf in the App_Data folder in Visual Studio with a table called Names.
How could I establish a connection to read the table values using C#?
So far I've tried something like this:
SqlConnection conn = new SqlConnection("Server=localhost;Database=Database1;");
conn.Open();
// create a SqlCommand object for this connection
SqlCommand command = conn.CreateCommand();
command.CommandText = "Select * from Names";
But I get an error:
database not found/error connecting to database

In Data Source (on the left of Visual Studio) right click on the database, then Configure Data Source With Wizard. A new window will appear, expand the Connection string, you can find the connection string in there

If you use SQL authentication, use this:
using System.Data.SqlClient;
SqlConnection conn = new SqlConnection();
conn.ConnectionString =
"Data Source=.\SQLExpress;" +
"User Instance=true;" +
"User Id=UserName;" +
"Password=Secret;" +
"AttachDbFilename=|DataDirectory|Database1.mdf;"
conn.Open();
If you use Windows authentication, use this:
using System.Data.SqlClient;
SqlConnection conn = new SqlConnection();
conn.ConnectionString =
"Data Source=.\SQLExpress;" +
"User Instance=true;" +
"Integrated Security=true;" +
"AttachDbFilename=|DataDirectory|Database1.mdf;"
conn.Open();

If you're using SQL Server express, change
SqlConnection conn = new SqlConnection("Server=localhost;"
+ "Database=Database1;");
to
SqlConnection conn = new SqlConnection("Server=localhost\SQLExpress;"
+ "Database=Database1;");
That, and hundreds more connection strings can be found at http://www.connectionstrings.com/

SqlConnection c = new SqlConnection(#"Data Source=localhost;
Initial Catalog=Northwind; Integrated Security=True");

You try with this string connection
Server=.\SQLExpress;AttachDbFilename=|DataDirectory|Database1.mdf;Database=dbname; Trusted_Connection=Yes;

I like to use the handy process outlined here to build connection strings using a .udl file. This allows you to test them from within the udl file to ensure that you can connect before you run any code.
Hope that helps.

Visual Studio 2019 (and probably a few previous versions).
View -> SQL Server Object Explorer
Top of the tree is 'SQL Server'
Under 'SQL Server', are couple of '(localdb)....'
Expand the (localdb)... -> Databases until you find your db.
Database Name (eg. Database1) -> Right-click -> Properties, and scroll the many properties (eg. "ANSI
NULL Default"). Find the "Connection string" property, copy the value
into your code, and you're running.