新人求助，请人帮助。

做到下面那个样本就ok了

var grade:char;
c,p,f:integer;
begin
repeat
write('enter a grade:');
readln(grade);
if grade<>'Z' then
case grade of
'A'..'C':begin
c:=c+1;
p:=p+1;
end;
'D'..'E':p:=p+1;
'F':f:=f+1;
end;
until grade='Z';
writeln('credit:',c,' ',(c/(p+f)):0:2);
writeln('pass:',p,' ',(p/(p+f)):0:2);
writeln('fail:',f,' ',(f/(p+f)):0:2);
end.