IBM Mainframes Interview Questions & Answers
Best IBM Mainframes Interview Questions and Answers
Dear Readers, Welcome to IBM Mainframes Interview Questions and Answers have been designed specially to get you acquainted with the nature of questions you may encounter during your Job interview for the subject of IBM Mainframes. These IBM Mainframes Questions are very important for campus placement test and job interviews. As per my experience good interviewers hardly plan to ask any particular questions during your Job interview and these model questions are asked in the online technical test and interview of many IT companies.
1. Name the divisions in a COBOL program.
IDENTIFICATION DIVISION, ENVIRONMENT DIVISION, DATA DIVISION, PROCEDURE DIVISION.
2. What are the different data types available in COBOL?
Alpha-numeric (X), alphabetic (A) and numeric (9).
3. What does the INITIALIZE verb do?
Alphabetic, Alphanumeric fields & alphanumeric edited items are set to SPACES.
Numeric, Numeric edited items set to ZERO.
FILLER , OCCURS DEPENDING ON items left untouched.
4. What is 77 level used for ?
Elementary level item. Cannot be subdivisions of other items (cannot be qualified), nor can they be subdivided themselves.
5. What is 88 level used for ?
For condition names.
6. What is level 66 used for ?
For RENAMES clause.
7. What does the IS NUMERIC clause establish ?
IS NUMERIC can be used on alphanumeric items, signed numeric & packed decimal items and usigned numeric & packed decimal items. IS NUMERIC returns TRUE if the item only consists of 0-9. However, if the item being tested is a signed item, then it may contain 0-9, + and - .
8. How do you define a table/array in COBOL?
01 ARRAYS.
05 ARRAY1 PIC X(9) OCCURS 10 TIMES.
05 ARRAY2 PIC X(6) OCCURS 20 TIMES INDEXED BY WS-INDEX.
9. Can the OCCURS clause be at the 01 level?
No.
10. What is the difference between index and subscript?
Subscript refers to the array occurrence while index is the displacement (in no of bytes) from the beginning of the array. An index can only be modified using PERFORM, SEARCH & SET. Need to have index for a table in order to use SEARCH, SEARCH ALL.
11. What is the difference between SEARCH and SEARCH ALL?
SEARCH - is a serial search.
SEARCH ALL - is a binary search & the table must be sorted ( ASCENDING/DESCENDING KEY clause to be used & data loaded in this order)
before using SEARCH ALL.
12. What should be the sorting order for SEARCH ALL?
It can be either ASCENDING or DESCENDING. ASCENDING is default. If you want the search to be done on an array sorted in descending order, then while defining the array, you should give DESCENDING KEY clause. (You must load the table in the specified order).
13. What is binary search?
Search on a sorted array. Compare the item to be searched with the item at the center. If it matches, fine else repeat the process with the left half or the right half depending on where the item lies.
14. My program has an array defined to have 10 items. Due to a bug, I find that even if the program access the 11th item in this array, the program does not abend. What is wrong with it?
Must use compiler option SSRANGE if you want array bounds checking. Default is NOSSRANGE.
15. How do you sort in a COBOL program? Give sort file definition, sort statement syntax and meaning.
Syntax:
SORT file-1 ON ASCENDING/DESCENDING KEY key....
USING file-2
GIVING file-3.
USING can be substituted by INPUT PROCEDURE IS para-1 THRU para-2
GIVING can be substituted by OUTPUT PROCEDURE IS para-1 THRU para-2.
file-1 is the sort workfile and must be described using SD entry in FILE SECTION.
file-2 is the input file for the SORT and must be described using an FD entry in FILE SECTION and SELECT clause in FILE CONTROL.
file-3 is the outfile from the SORT and must be described using an FD entry in FILE SECTION and SELECT clause in FILE CONTROL.
file-1, file-2 & file-3 should not be opened explicitly.
INPUT PROCEDURE is executed before the sort and records must be RELEASEd to the sort work file from the input procedure.
OUTPUT PROCEDURE is executed after all records have been sorted. Records from the sort work file must be RETURNed one at a time to the output procedure.
16. How do you define a sort file in JCL that runs the COBOL program?
Use the SORTWK01, SORTWK02,..... dd names in the step. Number of sort datasets depends on the volume of data being sorted, but a minimum of 3 is required.
17. How many Sections are there in Data Division?.
Ans: SIX SECTIONS 1.'FILE SECTION' 2.'WORKING-STORAGE SECTION' 3.'LOCAL-STORAGE SECTION' 4.'SCREEN SECTION' 5.'REPORT SECTION' 6.'LINKAGE SECTION'
In COBOL II, there are only 4 sections. 1.'FILE SECTION' 2.'WORKING-STORAGE SECTION' 3.'LOCAL-STORAGE SECTION' 4.'LINKAGE SECTION'.
18. Give the format of USING and GIVING in SORT statement. What are the restrictions with it?
See question 16. Restrictions - Cannot massage records, canot select records to be sorted.
19. What is the difference between performing a SECTION and a PARAGRAPH?
Performing a SECTION will cause all the paragraphs that are part of the section, to be performed.
Performing a PARAGRAPH will cause only that paragraph to be performed.
20. What is the use of EVALUATE statement?
Evaluate is like a case statement and can be used to replace nested Ifs.
The difference between EVALUATE and case is that no 'break' is required for EVALUATE i.e. control comes out of the EVALUATE as soon as one match is made.
21. What are the different forms of EVALUATE statement?
EVALUATE EVALUATE SQLCODE ALSO FILE-STATUS
WHEN A=B AND C=D WHEN 100 ALSO '00'
imperative stmt imperative stmt
WHEN (D+X)/Y = 4 WHEN -305 ALSO '32'
imperative stmt imperative stmt
WHEN OTHER WHEN OTHER
imperative stmt imperative stmt
END-EVALUATE END-EVALUATE
EVALUATE SQLCODE ALSO A=B EVALUATE SQLCODE ALSO TRUE
WHEN 100 ALSO TRUE WHEN 100 ALSO A=B
imperative stmt imperative stmt
WHEN -305 ALSO FALSE WHEN -305 ALSO (A/C=4)
imperative stmt imperative stmt
END-EVALUATE END-EVALUATE
22. How do you come out of an EVALUATE statement?
After the execution of one of the when clauses, the control is automatically passed on to the next sentence after the EVALUATE statement.
There is no need of any extra code.
23. In an EVALUATE statement, can I give a complex condition on a when clause?
Yes.
24. What is a scope terminator? Give examples.
Scope terminator is used to mark the end of a verb e.g. EVALUATE, END-EVALUATE; IF, END-IF.
25. How do you do in-line PERFORM?
PERFORM ... ...
END PERFORM
26. When would you use in-line perform?
When the body of the perform will not be used in other paragraphs. If the body of the perform is a generic type of code (used from various other places in the program), it would be better to put the code in a separate para and use PERFORM paraname rather than in-line perform.
27. What is the difference between CONTINUE & NEXT SENTENCE ?
CONTINUE is like a null statement (do nothing) , while NEXT SENTENCE transfers control to the next sentence (!!) (A sentence is terminated by a period)
28. What does EXIT do ?
Does nothing ! If used, must be the only sentence within a paragraph.
29. Can I redefine an X(100) field with a field of X(200)?
Yes. Redefines just causes both fields to start at the same location. For example:
01 WS-TOP PIC X(1)
01 WS-TOP-RED REDEFINES WS-TOP PIC X(2).
If you MOVE '12' to WS-TOP-RED,
DISPLAY WS-TOP will show 1 while
DISPLAY WS-TOP-RED will show 12.
30. Can I redefine an X(200) field with a field of X(100) ?
Yes.
31. What do you do to resolve SOC-7 error?
Basically you need to correcting the offending data.
Many times the reason for SOC7 is an un-initialized numeric item. Examine that possibility first.
Many installations provide you a dump for run time abends ( it can be generated also by calling some subroutines or OS services thru assembly language). These dumps provide the offset of the last instruction at which the abend occurred. Examine the compilation output XREF listing to get the verb and the line number of the source code at this offset. Then you can look at the source code to find the bug. To get capture the runtime dumps, you will have to define some datasets (SYSABOUT etc ) in the JCL. If none of these are helpful, use judgement and DISPLAY to localize the source of error.
Some installtion might have batch program debugging tools. Use them.
32. How is sign stored in Packed Decimal fields and Zoned Decimal fields?
Packed Decimal fields: Sign is stored as a hex value in the last nibble (4 bits ) of the storage.
Zoned Decimal fields: As a default, sign is over punched with the numeric value stored in the last bite.
33. How is sign stored in a comp-3 field?
It is stored in the last nibble. For example if your number is +100, it stores hex 0C in the last byte, hex 1C if your number is 101, hex 2C if your number is 102, hex 1D if the number is -101, hex 2D if the number is -102 etc...
34. How is sign stored in a COMP field ?
In the most significant bit. Bit is on if -ve, off if +ve.
35. What is the difference between COMP & COMP-3 ?
COMP is a binary storage format while COMP-3 is packed decimal format.
36. What is COMP-1? COMP-2?
COMP-1 - Single precision floating point. Uses 4 bytes.
COMP-2 - Double precision floating point. Uses 8 bytes.
37. How do you define a variable of COMP-1? COMP-2?
No picture clause to be given. Example 01 WS-VAR USAGE COMP-1.
38. How many bytes does a S9(7) COMP-3 field occupy ?
Will take 4 bytes. Sign is stored as hex value in the last nibble.
General formula is INT((n/2) + 1)), where n=7 in this example.
39. How many bytes does a S9(7) SIGN TRAILING SEPARATE field occupy ?
Will occupy 8 bytes (one extra byte for sign).
40. How many bytes will a S9(8) COMP field occupy ?
4 bytes.
41. What is the maximum value that can be stored in S9(8) COMP?
99999999
42. What is COMP SYNC?
Causes the item to be aligned on natural boundaries. Can be SYNCHRONIZED LEFT or RIGHT.
For binary data items, the address resolution is faster if they are located at word boundaries in the memory. For example, on main frame the memory word size is 4 bytes. This means that each word will start from an address divisible by 4. If my first variable is x(3) and next one is s9(4) comp, then if you do not specify the SYNC clause, S9(4) COMP will start from byte 3 ( assuming that it starts from 0 ). If you specify SYNC, then the binary data item will start from address 4. You might see some wastage of memory, but the access to this computational field is faster.
43. What is the maximum size of a 01 level item in COBOL I? in COBOL II?
In COBOL II: 16777215
44. How do you reference the following file formats from COBOL programs:
Fixed Block File - Use ORGANISATION IS SEQUENTIAL. Use RECORDING MODE IS F, BLOCK CONTAINS 0 .
Fixed Unblocked - Use ORGANISATION IS SEQUENTIAL. Use RECORDING MODE IS F, do not use BLOCK CONTAINS
Variable Block File - Use ORGANISATION IS SEQUENTIAL. Use RECORDING MODE IS V, BLOCK CONTAINS 0. Do not code the 4 bytes for record length in FD ie JCL rec length will be max rec length in pgm + 4
Variable Unblocked - Use ORGANISATION IS SEQUENTIAL. Use RECORDING MODE IS V, do not use BLOCK CONTAINS. Do not code 4 bytes for record length in FD ie JCL rec length will be max rec length in pgm + 4.
ESDS VSAM file - Use ORGANISATION IS SEQUENTIAL.
KSDS VSAM file - Use ORGANISATION IS INDEXED, RECORD KEY IS, ALTERNATE RECORD KEY IS
RRDS File - Use ORGANISATION IS RELATIVE, RELATIVE KEY IS
Printer File - Use ORGANISATION IS SEQUENTIAL. Use RECORDING MODE IS F,
BLOCK CONTAINS 0. (Use RECFM=FBA in JCL DCB).
45. What are different file OPEN modes available in COBOL?
Open for INPUT, OUTPUT, I-O, EXTEND.
46. What is the mode in which you will OPEN a file for writing?
OUTPUT, EXTEND
47. In the JCL, how do you define the files referred to in a subroutine ?
Supply the DD cards just as you would for files referred to in the main program.
48. Can you REWRITE a record in an ESDS file? Can you DELETE a record from it?
Can rewrite(record length must be same), but not delete.
49. What is file status 92?
Logic error. e.g., a file is opened for input and an attempt is made to write to it.
50. What is file status 39 ?
Mismatch in LRECL or BLOCKSIZE or RECFM between your COBOL pgm & the JCL (or the dataset label). You will get file status 39 on an OPEN.