Source Forms

Within a program, source code can be in free, fixed, or tab form. Fixed or tab forms must not be mixed with free form in the same source program, but different source forms can be used in different source programs.

All source forms allow lowercase characters to be used as an alternative to uppercase characters.

Several characters are indicators in source code (unless they appear within a comment or a Hollerith or character constant). The following are rules for indicators in all source forms:

• Comment indicator

  A comment indicator can precede the first statement of a program unit and appear anywhere within a program unit. If the comment indicator appears within a source line, the comment extends to the end of the line.

  An all blank line is also a comment line.

  Comments have no effect on the interpretation of the program unit.

  For more information, see comment indicators in free source form, or fixed and tab source forms.

• Statement separator

  More than one statement (or partial statement) can appear on a single source line if a statement separator is placed between the statements. The statement separator is a semicolon character (;).

  Consecutive semicolons (with or without intervening blanks) are considered to be one semicolon.

  If a semicolon is the first character on a line, the last character on a line, or the last character before a comment, it is ignored.

• Continuation indicator

  A statement can be continued for more than one line by placing a continuation indicator on the line. Intel Fortran allows at least 511 continuation lines for a fixed or tab source program. Although Standard Fortran permits up to 256 continuation lines in free-form programs, Intel® Fortran allows up to 511 continuation lines.

  Comments can occur within a continued statement, but comment lines cannot be continued.

  For more information, see continuation indicators in free source form, or fixed and tab source forms.

The following table summarizes characters used as indicators in source forms.

Indicators in Source Forms Source Item Indicator 1 Source Form Position Comment ! All forms Anywhere in source code Comment line ! Free At the beginning of the source line !, C, or * Fixed In column 1 Tab In column 1 Continuation line 2 & Free At the end of the source line Any character except zero or blank Fixed In column 6 Any digit except zero Tab After the first tab Statement separator ; All forms Between statements on the same line Statement label 1 to 5 decimal digits Free Before a statement Fixed In columns 1 through 5 Tab Before the first tab A debugging statement3 D Fixed In column 1 Tab In column 1 1 If the character appears in a Hollerith or character constant, it is not an indicator and is ignored. 2 For fixed or tab source form, at least 511 continuation lines are allowed. For free source form, at least 255 continuation lines are allowed. 3 Fixed and tab forms only.

Source form and line length can be changed at any time by using the FREEFORM, NOFREEFORM, or FIXEDFORMLINESIZE directives. The change remains in effect until the end of the file, or until changed again.

You can also select free source form by using compiler option free.

Source code can be written so that it is useable for all source forms.