How to specify a short int literal without casting?

Short answer, No. In C#, there’s no letter S that could be used as var a = 123S that would indicate that a is of type short. There’s L for long, F for float, D for double, M for decimal, but not S. It would be nice if there was, but there isn’t.

var a = 1M;  // decimal
var a = 1L;  // long
var a = 1F;  // float
var a = 1D;  // double
var a = 1;   // int

var a = 1U;  // uint
var a = 1UL; // ulong

but not

var a = 1S; // not possible, you must use (short)1;