PL/I Interview Questions (31 - 40)

31. How do you declare a structure in PL/I?

A structure is like a group of related variables. For example -

DCL 1 EMPLOYEE,
      2 ID FIXED BIN,
      2 NAME CHAR(20),
      2 SALARY FIXED DEC(7,2);

You can now refer to fields like EMPLOYEE.ID or EMPLOYEE.SALARY.

32. What is the purpose of the PICTURE attribute in PL/I?

PICTURE is used for formatted numeric data, especially when dealing with reports or input/output. For example -

DCL PRICE PICTURE 'ZZZ.99';

This formats a number with 3 digits before and 2 digits after the decimal. It helps you control the appearance of numbers.

33. How do you perform bit manipulation in PL/I?

Use bit variables and bit operations like AND, OR, XOR. For example -

DCL A BIT(8) INIT('10101010'B);
DCL B BIT(8) INIT('11001100'B);
C = A & B;  /* AND operation */

You can define BIT variables with BIT(n) where n is the number of bits.

34. What is the use of the UNION attribute in PL/I?

The UNION attribute allows multiple fields to share the same memory space. You can interpret the same data in different ways. For example -

DCL 1 DATA UNION,
      2 A FIXED BIN,
      2 B CHAR(4);

Here, A and B use the same storage — useful for low-level data manipulation or conversions.

35. How do you implement conditional compilation in PL/I?

Use %IF, %THEN, %ELSE for compile-time decisions.

%IF DEBUG %THEN
   PUT SKIP LIST('Debugging info');
%ELSE
   PUT SKIP LIST('Production mode');

You can control what parts of the program get compiled, depending on conditions like a DEBUG flag.

36. What are the different types of loops available in PL/I?

PL/I supports these types of loops:

• DO UNTIL: Loop runs first, then checks the condition.
• DO WHILE: Loop checks the condition first, then runs.
• DO n TO m: Repeats a fixed number of times.

37. How do you declare and use constants in PL/I?

Use the DEFINE statement to create constants:

%DECLARE PI CONSTANT FIXED DEC(5,4) VALUE(3.1416);

CONSTANT tells PL/I this value doesn't change. You can also use % constants for compile-time constants.

38. What is the difference between ALIGNED and UNALIGNED in PL/I?

• ALIGNED: Data is stored at memory boundaries that the system prefers. This is usually faster.
• UNALIGNED: Data can be stored anywhere in memory — more flexible, but sometimes slower.

DCL A FIXED BIN(31) ALIGNED;
DCL B FIXED BIN(31) UNALIGNED;

Use UNALIGNED if you’re reading binary data from files or hardware.

39. How do you perform recursion in PL/I?

To use recursion, declare the procedure as RECURSIVE.

RECURSIVE FACTORIAL(N)
   RETURNS(FIXED BIN(31)) =
   IF N <= 1 THEN RETURN(1);
   ELSE RETURN(N * FACTORIAL(N - 1));

Recursion is when a function calls itself to solve a smaller part of the problem.

40. What is the purpose of the REVERT statement in PL/I?

ON ERROR BEGIN;
   PUT SKIP LIST('An error occurred.');
END;

REVERT ERROR;  /* Turns off the ON ERROR handler */

Useful when you only want to handle an error for a limited section of code.

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