10.  Executable Statements

10.1.  IF-THEN-ELSE

• At last, the if-then-else branching structure has been added to Fortran. It is called a ``Block If''. A Block If begins with a statement of the form

  if ( . . . ) then
  

  and ends with an

  end if
  

  statement. Two other new statements may appear in a Block If. There may be several

  else if(. . .) then
  

  statements, followed by at most one

  else
  

  statement. If the logical expression in the Block If statement is true, the statements following it up to the next elseif, else, or endif are executed. Otherwise, the next elseif statement in the group is executed. If none of the elseif conditions are true, control passes to the statements following the else statement, if any. (The else must follow all elseifs in a Block If. Of course, there may be Block Ifs embedded inside of other Block If structures). A case construct may be rendered

  if (s .eq. 'ab') then
  . . .
  else if (s .eq. 'cd') then
  . . .
  else
  . . .
  end if
  

10.2.  Alternate Returns

• Some of the arguments of a subroutine call may be statement labels preceded by an asterisk, as in

  call joe(j, *10, m, *2)
  

  A return statement may have an integer expression, such as

  return k
  

  If the entry point has alternate return (asterisk) arguments and if , the return is followed by a branch to the corresponding statement label; otherwise the usual return to the statement following the call is executed.