If you use a positive seed, you can always replicate the stream of random numbers by using the same DATA step. If you use zero as the seed, the computer clock initializes the stream, and the stream of random numbers is not replicable. Every random-number function requires a seed value expressed as an integer constant, or a variable that contains the integer constant.
Every CALL routine calls a variable that contains the seed value.
Additionally, every CALL routine requires a variable that contains the generated random numbers. The seed variable must be initialized prior to the first execution of the function or CALL statement. After each execution of a function, the current seed is updated internally, but the value of the seed argument remains unchanged. After each iteration of the CALL statement, however, the seed variable contains the current seed in the stream that generates the next random number. With a function, it is not possible to control the seed values, and, therefore, the random numbers after the initialization.