Editing For loop (section)

===1957: FORTRAN===
{{Further|Fortran}}
Fortran's equivalent of the {{mono|for}} loop is the {{mono|DO}} loop,
using the keyword do instead of for,
The syntax of Fortran's {{mono|DO}} loop is:
<syntaxhighlight lang="fortranfixed">
        DO label counter = first, last, step
          statements
label     statement
</syntaxhighlight>
The following two examples behave equivalently to the three argument for-loop in other languages,
initializing the counter variable to 1, incrementing by 1 each iteration of the loop, and stopping at five (inclusive).
<syntaxhighlight lang="fortranfixed">
        DO 9, ICOUNT = 1, 5, 1
          WRITE (6,8) ICOUNT
    8     FORMAT( I2 )
    9   CONTINUE
</syntaxhighlight>
As of Fortran 90, block structured {{mono|END DO}} was added to the language.  With this, the end of loop label became optional:
<syntaxhighlight lang="Fortran">
do icounter = 1, 5
  write(*, '(i2)') icounter
end do
</syntaxhighlight>
The step part may be omitted if the step is one. Example:
<syntaxhighlight lang="fortranfixed">
* DO loop example.
       PROGRAM MAIN
         INTEGER SUMSQ
         SUMSQ = 0
         DO 199 I = 1, 9999999
           IF (SUMSQ.GT.1000) GO TO 200
199        SUMSQ = SUMSQ + I**2
200      PRINT 206, SUMSQ
206      FORMAT( I2 )
       END
</syntaxhighlight>

In Fortran 90, the {{mono|GO TO}} may be avoided by using an {{mono|EXIT}} statement.
<syntaxhighlight lang="fortranfixed">
* DO loop example.
       program main
         implicit none

         integer:: sumsq
         integer:: i

         sumsq = 0
         do i = 1, 9999999
           if (sumsq > 1000) exit
           sumsq = sumsq + i**2
         end do
         print *, sumsq

       end program
</syntaxhighlight>
Alternatively, a {{mono|DO - WHILE}} construct could be used:
<syntaxhighlight lang="fortranfixed">
       program main
         implicit none

         integer:: sumsq
         integer:: i

         sumsq = 0
         i = 0
         do while (sumsq <= 1000)
           i = i+1
           sumsq = sumsq + i**2
         end do
         print *, sumsq

       end program
</syntaxhighlight>