The following table lists the categories of operators, their symbols, and their meanings.

Operators

Category	Symbol	Operation
Arithmetic operators	+ - / * **	Addition or prefix plus Subtraction or prefix minus Division Multiplication Exponentiation
Relational (or comparison) operators	> < = ^> ^< ^= >= <=	Greater than Less than Equal to Not greater than Not less than Not equal to Greater than or equal to Less than or equal to
Bit-string (or logical) operators	^ (prefix) & | &: |: ^ (infix)	Logical NOT Logical AND Logical OR Logical AND THEN Logical OR ELSE Logical EXCLUSIVE OR
Concatenation operator	||	String concatenation

The following table gives the priority of PL/I operators. Low numbers indicate high priority. For example, the exponentiation operator (**) has the highest priority (1), so it is performed first, and the OR ELSE operator (|:) has the lowest priority (9), so it is performed last.

Precedence of Operators

Operator	Priority	Left/Right Associative	Order of Evaluation
()	0	N/A	deepest first
**	1	right	left to right
+ (prefix)	1	N/A	N/A
- (prefix)	1	N/A	N/A
^ (prefix)	1	N/A	N/A
*	2	left	left to right
/	2	left	left to right
+ (infix)	3	left	left to right
- (infix)	3	left	left to right
||	4	left	left to right
>	5	left	left to right
<	5	left	left to right
^>	5	left	left to right
^<	5	left	left to right
=	5	left	left to right
^=	5	left	left to right
<=	5	left	left to right
>=	5	left	left to right
&	6	left	left to right
|	7	left	left to right
^ (infix)	7	left	left to right
&:	8	left	left to right across entire expression
|:	9	left	left to right across entire expression

The following table discusses the contexts in which PL/I performs data conversion.

Contexts in Which PL/I Converts Data

Context	Conversion Performed
target = expression;	In an assignment statement, the given expression is converted to the data type of the target.
entry-name RETURNS (attribute...); . . .	In a RETURN statement, the specified value is converted to the data type specified by the RETURNS option on the PROCEDURE or ENTRY statement.
RETURN (value);
x + y x - y x * y x / y x**y x||y x & y x | y x&:y x|:y x ^ y x > y x < y x = y x^=y	In any expression, if operands do not have the required data type, they are converted to a common data type before the operation. For most operators, the data types of all operands must be identical. A warning message is issued in the case of a concatenation conversion.
BINARY (expression) BIT (expression) CHARACTER (expression) DECIMAL (expression) FIXED (expression) FLOAT (expression) OFFSET (variable) POINTER (variable)	PL/I provides built-in functions that perform specific conversions.
PUT LIST (item,...);	Items in a PUT LIST statement are converted to character-string data.
GET LIST (item,...);	Character-string input data is converted to the data type of the target item.
PAGESIZE (expression) LINESIZE (expression) SKIP (expression) LINE (expression) COLUMN (expression) format items A, B, E, F, and X TAB (expression)	Values specified for various options to PL/I statements must be converted to integer values.
DO control-variable...	Values are converted to the attributes of the control variable.
parameter	Actual parameters are converted to the type of the formal parameter if necessary.
INITIAL attribute	Initial values are converted to the type of the variable being initialized.

E.4 Pseudovariables

PL/I has the following pseudovariables:

• INT
• ONSOURCE
• ONCHAR
• PAGENO
• POSINT
• STRING
• SUBSTR
• UNSPEC

A pseudovariable can be used, in certain assignment contexts, in place of an ordinary variable reference. For example:

SUBSTR(S,2,1) = 'A';

This assigns the character <BIT_STRING>(A) to a 1-character substring of S, beginning at the second character of S.

A pseudovariable can be used wherever the following three conditions are true:

• The syntax specifies a variable reference.
• A value is explicitly assigned to the variable.
• The context does not require the variable to be addressable.

Pseudovariables are used most often in the following locations:

• The left side of an assignment statement
• The input target of a GET statement

Note that a pseudovariable cannot be used in preprocessor statements or in an argument list. For example:

CALL P(SUBSTR(S,2,1));

Here, SUBSTR is interpreted as a built-in function reference, not as a pseudovariable. The actual argument passed to procedure P is a dummy argument containing the second character of string S.

E.5 Built-In Subroutines

The following table summarizes the file-handling built-in subroutines.

Summary of File-Handling Built-In Subroutines

Subroutine	Function
DISPLAY	Returns information about a file.
EXTEND	Allocates additional disk blocks for a file.
FLUSH	Requests the file system to write all buffers onto disk to preserve the current status of a file.
FREE	Unlocks all the locked records in a file.
NEXT_VOLUME	Begins processing the next volume in a multivolume tape set.
RELEASE	Unlocks a specified record in a file.
REWIND	Positions a file at its beginning or at a specific record.
SPACEBLOCK	Positions a file forward or backward a specified number of blocks.

PL/I also has the condition-handling subroutine RESIGNAL. This subroutine allows an ON-unit to pass on a condition signal and causes the condition to be resignaled for handling by a different ON-unit.