How to insert special chracter in SQL datbase through web service

string q = "insert into log(@code,@input) values ('" + src.ToString()+ "','" + input.ToString() + "')";

possibly a solution to your question.
Never build an SQL query by concatenating strings. Sooner or later, you will do it with user inputs, and this opens door to a vulnerability named "SQL injection", it is dangerous for your database and error prone.
A single quote in a name and your program crash. If a user input a name like "Brian O'Conner" can crash your app, it is an SQL injection vulnerability, and the crash is the least of the problems, a malicious user input and it is promoted to SQL commands with all credentials.
SQL injection - Wikipedia[^]
SQL Injection[^]
SQL Injection Attacks by Example[^]
PHP: SQL Injection - Manual[^]
SQL Injection Prevention Cheat Sheet - OWASP[^]

By using parameters you will be able to insert the special characters. For example:

private void InsertMethod(string code, string input)
{
  using (var conn = new SqlConnection(ConnectionString))
  {
    con.Open();
    var myQuery = "insert into [log] ([code],[input]) values (@code, @input)";
    var paramCode = new SqlParameter("@code", SqlDbType.NVarChar) {Value = code};
    var paramInput = new SqlParameter("@input", SqlDbType.NVarChar) {Value = input};     
    using (var cmd = new SqlCommand(myQuery conn))
    {
      cmd.Parameters.Add(paramCode);
      cmd.Parameters.Add(paramInput);

      cmd.ExecuteNonQuery()
    }
  }
}

In this example I use the SqlDbType.NVarChar. You can use a whole series of types that of course should match you table structure.