Finding the largest observation

There might be many ways to do this. A simple way would be to as follows:

data new;
Infile '/udd/n2man/epimarks/classmarks.txt';
input roll 4. ExamDate MMDDYY10. @17 MidFinal $2. Marks 4.;
obsno=_n_;
/* creates a new variable obsno whose value is the same as observation number in the dataset */

proc univariate;
var marks;
run;

/* see the observation number for the largest variable(s) in the output. Run the program again with following added*/

proc print;
where obsno=15; /* 15 is the obsno from the output of proc univariate */

A sophisticated way

data new2;
Infile '/udd/n2man/epimarks/classmarks.txt';
input roll 4. ExamDate MMDDYY10. @17 MidFinal $2. Marks 4.;

proc sort data =new2;
by descending marks;

data _null_ ; /* null datasets only exist for the particular datastep where they are called */
set new2 ;
If _n_=1 then call symput("IDNumber",Roll);
/* this creates a macro variable IDNumber whose value is the roll of the first observation which is the one with largest marks because of sorting*/
else stop;

proc print data=new2;
where Roll="&IDnumber";
format ExamDate WORDDATE18.;
title "Student &IDNumber Had the highest marks ";
run;