How to return a value using constructor in c#?

Constructors do not have a return type, but you can pass values by reference using the ref keyword. It would be better to throw an exception from the constructor to indicate a validation failure.

public class YourClass
{
    public YourClass(ref string msg)
    {
         msg = "your message";
    }

}    

public void CallingMethod()
{
    string msg = string.Empty;
    YourClass c = new YourClass(ref msg);       
}

The constructor does return a value - the type being constructed...

A constructor is not supposed to return any other type of value.

When you validate in a constructor, you should throw exceptions if the passed in values are invalid.

public class MyType
{
    public MyType(int toValidate)
    {
      if (toValidate < 0)
      {
        throw new ArgumentException("toValidate should be positive!");
      }
    }
}

Make a Constructor with Out parameter and send your return value via same.

public class ClassA
{
    public ClassA(out bool success)
    {
        success = true;
    }
}