2.2 Structure of conditional Fortran code

Lines which begin cstart, celse, cend and c; are treated specially by ftc.

1. cstart can be followed by a keyword, and if the flag corresponding to the keyword is true, all code up to the next cend is forced active, i.e., any leading c; is stripped away. If, conversely, the flag is false, all code up to cend is forced inactive, inserting c; as necessary. celse can be used to implement alternatives in an obvious way, for example,

    cstart unix-i8
    c;      write (6,*) 'Integer length is 8'
    celse
         write (6,*) 'Integer length is 4'
    cend
   

2. More than one keyword can be given on the cstart line, with a logical or being assumed between each. If the requirement is for two flags to be set for the code to be active, the keywords may be separated by .and.; keywords may be preceded by .not.. For example,

    cstart cray .and. .not. mpp
          write (6,*) 'This is a Cray, but not MPP'
    cend
   

3. cstart $\dots$ cend constructs may be nested up to some reasonable limit.