CMPR2

When the program is called for the first time, the PERFORM statement will be executed. If the "N > 1" test succeeds, the program will return to the calling program.

However, this means that the PERFORM statement has not reached normal completion because paragraph A never returned to the point from which it was performed. The compiler-generated mechanism at the end of paragraph A is still "set" to return back to the PERFORM statement.

Thus, on the second call to the program, the ELSE path will be taken, 1 will be subtracted from N, and control will be transferred by the GO TO statement to paragraph A. However, if the test "N > 1" fails, the PERFORM mechanism is still set. So, when the end of paragraph A is reached, instead of falling through into paragraph B, control is "returned" to the MOVE statement after the PERFORM statement.

These results might not be intended. The problem might occur whenever all of the following conditions occur:

1. The program returns to the calling program with an EXIT PROGRAM or GOBACK statement.
2. A PERFORM statement performs a paragraph or a range of paragraphs, and those paragraphs might also be reached by a GO TO statement or by falling through into the paragraph.
3. All such PERFORM statements have not had a chance to return prior to the execution of the EXIT PROGRAM or GOBACK statement.