Appendix C — Operator precedence & the collating sequence

Operator precedence

From highest (binds tightest) to lowest (§6). Within a level, evaluation is left-to-right, except **, which is right-to-left.

Rank	Operators	Notes
1 (highest)	**	exponentiation; right-associative (2**3**2 = 2**(3**2))
2	* /	multiply, divide
3	unary + -, binary + -	(so -A**2 = -(A**2))
4	//	character concatenation
5	.LT. .LE. .EQ. .NE. .GT. .GE.	relational (yield logical)
6	.NOT.	logical negation
7	.AND.	logical and
8	.OR.	logical or
9 (lowest)	.EQV. .NEQV.	logical equivalence / non-equivalence

Across families this is the ladder arithmetic > character > relational > logical, so 2 + 3 .GT. 4 is (2+3) .GT. 4 and needs no parentheses. You may not place two operators adjacently — write A**(-B), not A**-B. Parenthesized subexpressions are evaluated as written and not regrouped.

The collating sequence

Character comparison (.LT., the LGE/LGT/LLE/LLT intrinsics, etc.) uses a collating sequence. The standard requires only a partial order (§3.1.5):

• A < B < … < Z,
• 0 < 1 < … < 9,
• blank is less than both A and 0,
• the letters and digits are not interleaved (all digits precede A, or all follow Z).

.EQ. and .NE. do not depend on the collating sequence. When two character operands differ in length, the shorter is blank-padded on the right before comparison, so 'HI' equals 'HI '.

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forterp notes. forterp uses the ASCII collating sequence, which satisfies the standard's partial order (in ASCII: blank 32, digits 48–57, upper-case letters 65–90 — so blank < digits < letters). ICHAR/CHAR therefore map to ASCII codes.