Overview

In COBOL, understanding the difference between the CALL and EXECUTE statements is crucial for program control and modular coding practices. This distinction is pivotal in how subprograms are invoked and managed, influencing program structure, reusability, and performance.

Key Concepts

1. Modularity and Reusability: Using CALL and EXECUTE enhances the modularity and reusability of COBOL programs.
2. Parameter Passing: Different methods of parameter passing and their implications on program behavior.
3. Performance Considerations: How each statement impacts the program's execution time and resource utilization.

Common Interview Questions

Basic Level

1. What is the basic difference between CALL and EXECUTE statements in COBOL?
2. How do you pass parameters using the CALL statement?

Intermediate Level

3. Explain the performance implications of using CALL versus EXECUTE.

Advanced Level

4. Discuss how CALL and EXECUTE influence modular programming and code reusability in COBOL.

Detailed Answers

1. What is the basic difference between CALL and EXECUTE statements in COBOL?

Answer: In COBOL, CALL is used to invoke a subprogram or an external program, where control is transferred to the called program and returns back to the calling program once the execution is completed. The EXECUTE statement, on the other hand, is not a standard COBOL statement for invoking programs but is often confused with SQL's EXECUTE or the EXECUTE interface used in integrating COBOL with other languages or systems, such as DB2 SQL commands.

Key Points:
- CALL is a COBOL statement for program invocation.
- EXECUTE often refers to executing SQL queries from COBOL or external command execution but is not a COBOL statement for calling programs.
- Misunderstanding or misuse of these terms can lead to confusion about their functionality and usage in COBOL.

Example:

CALL 'SUBPROGRAM' USING ARGUMENTS.

This COBOL line demonstrates a basic CALL to a subprogram with arguments.

2. How do you pass parameters using the CALL statement?

Answer: Parameters in COBOL can be passed using the USING clause of the CALL statement. This allows the main program to pass data to the subprogram, which can then use or modify this data and return it back to the calling program.

Key Points:
- Parameters can be passed by reference, by content, or by value.
- Passing by reference is the most common and allows the called program to modify the original data.
- Passing by content or value protects the original data from being altered by the called program.

Example:

CALL 'CALCULATE' USING BY REFERENCE NUM1 BY VALUE NUM2.

This example demonstrates passing NUM1 by reference, allowing CALCULATE to modify its value, and NUM2 by value, protecting its original content.

3. Explain the performance implications of using CALL versus EXECUTE.

Answer: The CALL statement, when referring to performance, entails a certain overhead due to the necessity of transferring control and possibly loading an external program into memory. The performance impact of an EXECUTE statement largely depends on its context (e.g., executing a SQL query versus a system command), which can vary widely in terms of execution time and resource usage.

Key Points:
- CALL may introduce overhead from loading external programs.
- EXECUTE performance varies greatly based on context but in database operations can introduce significant overhead due to query execution and data retrieval.
- Efficient use of either requires understanding their context and optimizing their use accordingly.

4. Discuss how CALL and EXECUTE influence modular programming and code reusability in COBOL.

Answer: CALL enhances modular programming and code reusability by allowing programs to be broken into smaller, manageable subprograms that can be reused across different parts of a COBOL application or even in different applications. While EXECUTE is not directly a COBOL statement for modular programming, the concept of executing external commands or queries supports integrating COBOL applications with external systems or databases, thereby extending the modularity beyond COBOL itself.

Key Points:
- CALL promotes code modularity and reusability within COBOL applications.
- EXECUTE, in its relevant contexts, allows COBOL programs to leverage external systems or databases, thus extending modularity.
- Together, they support building flexible, maintainable, and scalable COBOL applications.

Note: It's important to clarify that EXECUTE in the context of COBOL often relates to interfacing with external systems or executing SQL queries, rather than a direct counterpart to CALL for program control.