I believe you want to process first 50 jcl statements out of total 100,
if this is what you want to do, you can do this by making 51st statement
of your jcl as null statement.
i.e. 51st statement should be like
//
And by your second question what I understand is you are looking for a
cobol program using vsam data set. For this you can refer to the
programs section of this forum.