Insert numerical (decimal) data from textbox values

Question

I am confused by the following issue;

I have a C# (WindowsForms) application which I connect to a SQL Server DB and have no problem to INSERT, SELECT, UPDATE... until I

Answer 1

This is not a direct answer to your question, but please (!) replace this ugly method by this:

Create a class for your contracts. This will make it much easier to handle contracts. If you have several methods handlings contracts in some way, you will not have to change the almost endless parameter lists of all of them, when properties are added to the contract.

public class Contract
{
    public int EmployeeID { get; set; }
    public string Agency { get; set; }
    public string Role { get; set; }
    ... and so on
}

and change the method signature to

public void CreateNewContract(Contract contract)

Headers of methods loading contracts form the database would look like this

public List LoadAllContracts()

// Assuming contractID is the primary key
public Contract LoadContractByID(int contractID)

Much easier than returning 1000 variables!

You can create a new contract with

var contract = new Contract {
    EmployeeID = 22,
    Agency = "unknown",
    Role = "important", 
    ...
};

---

Also (as others have pointed out already) use command parameters.

newCmd.Parameters.AddWithValue("@EmployeeID", contract.EmployeeID);
newCmd.Parameters.AddWithValue("@Agency", contract.Agency);
newCmd.Parameters.AddWithValue("@Role", contract.Role);

(HaLaBi's post shows how to formulate your insert command string.)