using System.Linq;



DirectoryInfo directoryInfo = new DirectoryInfo(@"path to code");
var files = directoryInfo.GetFiles("*.cs", SearchOption.AllDirectories)
                .Union(directoryInfo.GetFiles("*.ts", SearchOption.AllDirectories))
                .Union(directoryInfo.GetFiles("*.scss", SearchOption.AllDirectories))
                .Union(directoryInfo.GetFiles("*.html", SearchOption.AllDirectories));

int linesCount = files.Select(f => File.ReadAllText(f.FullName))
                    .Aggregate((current, next) => current + next)
                    .Split("\n")
                    .Length;

Console.WriteLine(linesCount);