In SAP ABAP programming, what is the key difference between using CALL SCREEN and using LEAVE SCREEN in a dialog program?

Introduction / Context:
In SAP ABAP dialog programming, navigation between screens is very important. Developers often use statements such as CALL SCREEN and LEAVE SCREEN to control how the user moves through a transaction. Understanding the difference between these two statements helps you design user flows that are predictable and supportable, especially when multiple dialog screens are linked together in one program.

Given Data / Assumptions:

• We are working in an SAP ABAP dialog program that uses classic dynpro screens.
• CALL SCREEN and LEAVE SCREEN are both valid ABAP control statements.
• The question is about how control flows between screens and back to the caller.
• We assume a basic knowledge of PBO and PAI events on screens.

Concept / Approach:
CALL SCREEN starts a new screen as if you temporarily branch from the current screen, then come back when the called screen is closed. You can imagine a stack of screens where the calling screen waits underneath. LEAVE SCREEN, by contrast, tells the runtime system to end processing of the current screen and continue with the next screen in the defined flow logic, without automatically returning. This means CALL SCREEN creates a call and return pattern, while LEAVE SCREEN is more like a forward jump in the dialog flow.

Step-by-Step Solution:
Step 1: Identify what CALL SCREEN does. It opens a new screen and suspends the current one until the called screen finishes. Step 2: When the user leaves the called screen, control returns to the original screen after the CALL SCREEN statement. Step 3: Identify what LEAVE SCREEN does. It ends the processing of the current screen at the next opportunity and continues with the next screen according to the screen flow logic or program logic. Step 4: Note that LEAVE SCREEN does not build a stack of screens to which control returns automatically. Step 5: Compare the options and select the one that clearly describes CALL SCREEN with return and LEAVE SCREEN as a one way move to the next screen.

Verification / Alternative check:
In ABAP documentation and many training materials, CALL SCREEN is explained as a statement that calls another screen like a subroutine, and after the user exits that screen, control comes back to the calling screen. LEAVE SCREEN, in contrast, is described as terminating the current screen and moving on in the sequence. This matches the description in option a and confirms that it is the correct conceptual explanation.

Why Other Options Are Wrong:
Option b incorrectly claims that CALL SCREEN exits the program and LEAVE SCREEN terminates the entire session, which is not accurate. Option c ties CALL SCREEN only to background jobs and LEAVE SCREEN only to dialog programs, which has no basis. Option d says they behave exactly the same, which ignores the call and return behavior of CALL SCREEN. Option e mislabels them as list or selection screen only, which is also incorrect.

Common Pitfalls:
A common mistake is to use LEAVE SCREEN expecting to come back to the same place in code, which does not happen. Another pitfall is overusing nested CALL SCREEN statements without a clear navigation design, which can confuse users. Remembering that CALL SCREEN returns and LEAVE SCREEN moves forward helps avoid logical navigation errors.

Final Answer:
The key difference is that CALL SCREEN opens another screen and then returns to the caller when the user leaves it, while LEAVE SCREEN ends processing of the current screen and continues with the next screen in the flow without returning.