COBOL Tricky Interview Question: Processing of 2 Files

Here are COBOL scenario based interview questions. If the domain is Banking, surely this question you can expect in interview. Click to read on Banking domain knowledge.

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How to process 2 files by comparing key fields in COBOL?


  • Read the records in both the first file and the second file. If the key field matches, you can ignore it.
  • Let us say T, M files.
  • T < M means this is a new account so we need to update in the master file
  • T > M means an account is missing in the Master file, so we need to update it


  • If both files are the same number of records. It is good, our work is reduced
  • If T file comes to AT END you need to move HIGH VALUES into the key field
  • If M files come to  AT END you need to move HIGH VALUES into the key field
  • So you need to process till both key fields are equal to HIGH VALUES.

Note: Key fields must be in PIC (X) not numeric


  • To avoid a lot of I/Os, you can read data into a local array table, and you can process the records.

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Author: Srini

Experienced software developer. Skills in Development, Coding, Testing and Debugging. Good Data analytic skills (Data Warehousing and BI). Also skills in Mainframe.