C# check if you have passed arguments or not

if(args.Length==0) should work, args[0] requires at least one argument to not crash.

if(args == null || args.Length == 0)
{
    // no arguments
}
else
{
    // arguments
}

it's an array and there's two scenarios that might have the meaning NO arguments passed. Depending on your semantics

args == null or args.Length == 0

In this case where the method is called when the program is executed (e.g. not calling the method as part of say a unit test) the args argument will never be null (making the first test redundant) I've included it for completeness because the same situation might easily be encountered in other methods than main

if you test them in that order you don't have to worry about args being null in the latter expression

if(args == null || args.Length == 0){
    ComputeNoParam cptern = new ComputeNoParam();
    cptern.ComputeWithoutParameters();
}
else
{
    ComputeParam cpter = new ComputeParam();
    foreach (string s in args){...}
}