Mainframes Interview Questions
1. 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).
2. 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 – .
3. 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.
4. 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.
5. How do you sort in a COBOL program? Give sort file definition, sort statement syntax and meaning?
SORT file-1 ON ASCENDING/DESCENDING KEY key….
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.
6. 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.
7. 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.
8. 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.
9. What do you do to resolve SOC-7 error?
Basically you need to correct 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.
10.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.