The DO statement controls a block of statements which are executed repeatedly, once for each value of a variable called the loop-control variable. The number of iterations depends on the parameters of the DO statement at the heads of the loop. The first item after the keyword ``DO" is the label which is attached to the last statement of the loop. For example:
*Sum the squares of the first N elements of the array X SUM = 0.0 DO 15, I = 1,N SUM = SUM + X(I)**2 15 CONTINUEIf we had wanted only to sum alternate elements of the array we could have used a statement like:
DO 15,I = 1,N,2
DO 100,I = 5,1,-1 WRITE(UNIT=*,FMT=*) I**2 100 CONTINUEwill produce 5 records containing the values 25, 16, 9, 4, and 1 respectively.
Loops can be nested to any reasonable depth. Thus the following statements will set the two dimensional array FIELD to zero.
REAL FIELD(NX, NY) DO 50, IY = 1,NY DO 40, IX = 1.NX FIELD(IX,IY) = 0.0 40 CONTINUE 50 CONTINUE