complex number & sort

hi everbody , i have 3 questions :

1) i know how complex number must be written in fortran . but now i
want to
calculate complex number in loop and use its value for other parts ,
my problem is
with complex number in loop . for example , i guess with this way i
work with complex numbers :

complex m

do i=1,10,1
end do

this program doesn't work .what can i do ?

2) i have an array with dimensioins A(3,200) . i want to sort these
with increasing the second row data algebrically . in fortran
libarary i can't
find suitable program , all program are for vectors .can anybody
propose me a way ?

3) in my program , numbers are calculated with 6 digits precesion
after point .( for example 21.938495 ) how
can i control the precesion ? i want it computes with 3 or 2 digits
after point .

best ,nakisa