How to inject code to a .net windows forms application

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C#

VB

.NET

i want to inject some code into .net assemblies such as { windows forms application }

i think mono.cecil is a useful reference tool ,but i can't work whit it :(

my code i would to inject to a win forms application is :

public class Program
{
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        Application.Run(new myloginForm());
    }
}

thanks.