COBOL PERFORM A THRU A EXIT笔误 COMPUTE +或- 笔误 结果分析

1、COMPUTE A = + B，A = - B 一般为笔误，执行结果：A的值等于|B|。
测试:
MOVE 5 TO WK-INPUT
MOVE 5 TO WK-OUTPUT
或者
MOVE -5 TO WK-INPUT
MOVE -5 TO WK-OUTPUT
COMPUTE WK-OUTPUT = + WK-INPUT
执行结果：WK-OUTPUT结果为5.
COMPUTE WK-OUTPUT = - WK-INPUT
执行结果：WK-OUTPUT结果为5.

2、THRU笔误：编译测试均通过
以下包括THRU执行流程、THRU笔误执行测试。
如下笔误：
……                                                          ==> 该部分代码正常执行
PERFORM XXXX-TEST-PREFORM
   THRU XXXX-TEST-PREFORM EXIT  ==> 红色字为COBOL关键字 不执行XXXX-TEST-PROFORM-EXIT
……                                                          ==> 该部分代码正常执行
XXXX-TEST-PROFORM-EXIT.
    EXIT.
上述语句编译成功，不影响正常程序流，程序执行步骤完全一致，所有测试全部通过。
EXIT语句，其实就是标识而已，不起作用。

若XXXX-TEST-PROFORM-EXIT写法如下，执行结果会有很大不同。若写法如下，可能是程序退出点，但因为未正确书写“THRUXXXX-TEST-PROFORM-EXIT”，则程序不会执行该段，导致程序无法退出。
XXXX-TEST-PROFORM-EXIT.
    GOBACK./STOP RUN.

测试程序如下：
PROCEDURE DIVISION.                                       
*                                                          
MAIN-ROUTINE.                                             
*                                                          
     DISPLAY 'MAIN ROUTINE START'.                         
*                                                          
     PERFORM A-ROUTINE                                     
        THRU A-ROUTINE-EXIT                                
*                                                          
     DISPLAY '== START EXEC A-C ROUTINE =='.               
     PERFORM A-ROUTINE                                     
        THRU C-ROUTINE-EXIT                                
     DISPLAY '== END EXEC A-C ROUTINE =='.                 
*                                                          
     PERFORM B-ROUTINE                                     
        THRU B-ROUTINE-EXIT                                
*                                                          
     PERFORM C-ROUTINE                                     
        THRU C-ROUTINE EXIT                                
     DISPLAY 'C-ROUTINE EXIT IN MAIN'.                     
*                                                          
     PERFORM C-ROUTINE                                     
        THRU C-ROUTINE-EXIT                                
     DISPLAY 'C-ROUTINE-EXIT IN MAIN'.                
*                                                     
     PERFORM D-ROUTINE                                
        THRU D-ROUTINE-EXIT                           
*                                                     
     DISPLAY 'MAIN ROUTINE END'.                      
MAIN-ROUTINE-EXIT.                                   
     STOP RUN.                                        
*                                                     
A-ROUTINE.                                           
     DISPLAY 'EXEC A ROUTINE'.                        
A-ROUTINE-EXIT.                                      
     DISPLAY 'EXEC A ROUTINE EXIT'.                   
     EXIT.                                            
*                                                     
B-ROUTINE.                                           
     DISPLAY 'EXEC B ROUTINE'.                        
B-ROUTINE-EXIT.                                      
     DISPLAY 'EXEC B ROUTINE EXIT'.                   
     EXIT.                                            
*                                                     
C-ROUTINE.                                           
     DISPLAY 'EXEC C ROUTINE'.                        
C-ROUTINE-EXIT.                        
     DISPLAY 'C-ROUTINE-EXIT IN C'.     
     EXIT.                              
*                                       
D-ROUTINE.                             
     DISPLAY 'EXEC D ROUTINE'.          
D-ROUTINE-EXIT.                        
     DISPLAY 'EXEC D ROUTINE EXIT'.     
     EXIT.                              
*                                      

执行结果如下：
MAIN ROUTINE START         
EXEC A ROUTINE             
EXEC A ROUTINE EXIT        
== START EXEC A-C ROUTINE ==
EXEC A ROUTINE             
EXEC A ROUTINE EXIT        
EXEC B ROUTINE             
EXEC B ROUTINE EXIT        
EXEC C ROUTINE             
C-ROUTINE-EXIT IN C        
== END EXEC A-C ROUTINE == 
EXEC B ROUTINE             
EXEC B ROUTINE EXIT        
EXEC C ROUTINE             
C-ROUTINE EXIT IN MAIN     
EXEC C ROUTINE             
C-ROUTINE-EXIT IN C        
C-ROUTINE-EXIT IN MAIN     
EXEC D ROUTINE             
EXEC D ROUTINE EXIT        
MAIN ROUTINE END          

转自:http://hi.baidu.com/clisdena/item/01857711271c686c70d5e8d0

3,
       IDENTIFICATION DIVISION.
       PROGRAM-ID. PGM012.
       AUTHOR. MAINFRAMEWIZARD.
       DATA DIVISION.
       WORKING-STORAGE SECTION.
       01 WS-SUB PIC 9(3) VALUE ZEROS.
       PROCEDURE DIVISION.
       10000-MAIN-PARA.
             PERFORM 20000-FIRST-PARA THRU 30000-THIRD-PARA
             DISPLAY 'DEPICTING PERFORM THRU BY MAINFRAMEWIZARD.COM'
             DISPLAY 'PARA NAME IS  10000-FIRST-PARA'
             STOP RUN.
       20000-FIRST-PARA.
             DISPLAY 'PARA NAME IS  20000-FIRST-PARA'.
       25000-SECOND-PARA.
             DISPLAY 'PARA NAME IS  25000-SECOND-PARA'.
       30000-THIRD-PARA.
             DISPLAY 'PARA NAME IS  30000-THIRD-PARA'


Output of the above program is as below



PARA NAME IS  20000-FIRST-PARA                                                                                          
PARA NAME IS  25000-SECOND-PARA                                                                                         
PARA NAME IS  30000-THIRD-PARA                                                                                          
DEPICTING PERFORM THRU BY MAINFRAMEWIZARD.COM                                                                           
PARA NAME IS  10000-FIRST-PARA                                     
- See more at: http://www.mainframewizard.com/content/cobol-perform-thru#sthash.SBBE20eI.dpuf