Delete all elements in an array that are equal to the given number.

 

Question:; in the additional segment, there is a list of unordered word groups with the first address, which is stored in the length of the array in the first of the array, the first address of the array is included in the di register. There is a number in the ax register.
Requirement: compile a program to search for this number in the array. If this number is found, delete it from the array.

Train of Thought: the analysis of this array may contain more than one element equal to this number, but may not have one. It can be implemented in the same way as below:

First, find the first element equal to the number:

1> exit the operation if there are no equal elements.

2> If an equal element exists and the position Si of the element is recorded at the same time, and the element is deleted, you can move the subsequent element forward,

3> when moving forward, consider whether it is equal to this number,

A. If they are equal, no other processing is performed except for moving forward the cursor di pointing to the post element.

B. If not, it is transmitted to the position indicated by Si, and then Si and Di are moved forward simultaneously.

All elements in the Goto 3 and until arrays are traversed.

Implementation: considering that string search commands combined with repeated prefix repe/repz or repne/repnz can implement the search function:

SCAs ES: [di]: Operation on the target address

Scasb: Performs byte operations and implements the following functions:

(Al)-(DI), if df = 0 as CLD, (DI) <---- (DI) + 1, else df = 1 as STF, (DI) <------ (DI)-1

Scasw: The following functions are implemented for word operations:

(Ax)-(dx), if df = 0 as CLD, (DI) <---- (DI) + 2, else df = 1 as STF, (DI) <------ (DI)-2

Command function: the command compares the content of Al (or ax) with a byte (or word) in the additional segment specified by (DI), but does not save the result, only the result is configured with a condition code (that is, the value of the program status word: psw ).

The preceding commands are usually combined with the repeated prefix repe/repz or repne/repnz to compare two data strings or find the specified data in a data string.

The rep prefix is usually used in combination with the movs (string transmission, movsb, movsw), STOs (string storage, stosb, stosw), and lods (get string, lodsw, lodsb) commands.

Format: rep command

Function: 1. test whether the Cx value is 0. If the value is 0, exit the execution of the command and execute the next command of the command; otherwise, go to 2,

2. (CX) <------ (CX)-1

3. Execute the subsequent commands

4. Repeat the 1.2.3 operation

In addition to testing CX, repe/repz or repne/repnz with a duplicate prefix with a condition code, it also tests the setting of the condition code after executing the command (that is, the effect on psw, ZF flag changes)

Do not confuse the association of repeated prefixes with instructions.

There is also a jump command: The jcxz label is worth mentioning to test whether the Cx is 0, and if it is 0, it is transferred to the specified number.

Code:

1. In the additional segment, there is an unsorted word group whose first address is list, and the first address of the array is stored in the length of the array. The first address of the array has been placed in the di register. There is a number in the ax register.
2. ; Requirement: compile a program to search for this number in the array. If this number is found, delete it from the array.
4. Data Segment
5. Number DW 9 h
7. Data ends
9. Extra segment
10. List DW 0ah, 01 H, 9 h, 3 h, 4 h, 5 h, 9 h, 6 h, 9 h, 0ah, 9 h
11. Extra ends
13. Code segment
14. Assume DS: data, ES: Extra, CS: Code
16. Start:
17. MoV ax, Data
18. MoV ds, ax
19. MoV ax, extra
20. MoV es, ax
22. MoV Di, offset list
23. MoV ax, number
25. MoV dx, 0
26. MoV CX, ES: [di]
27. Add Di, 2
28. ClD
30. Repne scasw
32. Jcxz exit
34. INC DX
35. MoV Si, Di
36. Sub Si, 2
37. Lo:
38. CMP ax, ES: [di]
39. JNE next
40. INC DX
41. JMP next1
43. Next:
44. MoV BX, ES: [di]
45. MoV ES: [Si], BX
46. Add Si, 2
47. Next1:
48. Add Di, 2
49. Loop Lo
51. Exit:
52. Sub ES: list [0], DX
53. ; Xchg ES: list [0], DX
55. Add DL, 30 h
56. MoV ah, 02 h
57. Int 21 h
59. MoV ah, 4ch
60. Int 21 h
62. Code ends
63. End start

After note:

Code:

1. ; In the additional segment, there is a list of unordered word groups with the first address, which is stored in the length of the array in the first of the array, the first address of the array is included in the di register. There is a number in the ax register.
2. ; Requirement: compile a program to search for this number in the array. If this number is found, delete it from the array.
4. Data Segment
5. Number DW 9 h
7. Data ends
9. Extra segment
10. List DW 0ah, 01 H, 9 h, 3 h, 4 h, 5 h, 9 h, 6 h, 9 h, 0ah, 9 h
11. Extra ends
13. Code segment
14. Assume DS: data, ES: Extra, CS: Code
16. Start:
17. MoV ax, Data
18. MoV ds, ax
19. MoV ax, extra
20. MoV es, ax
22. MoV Di, offset list
23. MoV ax, number
25. MoV dx, 0; use to store the number of equal elements
26. MoV CX, ES: [di]; MoV the number of the array's elements to CX
27. Add Di, 2; Set di as the address of the first element
28. CLD; set the DF of psw to 0, the direction is up
30. Repne scasw; scan the number in ax, until Cx = 0 or find the First Equal Element
32. Jcxz exit; can't find the equal element in the array, Goto exit
34. Inc dx; make the number of equal elements increase 1, as one has been found
35. MoV Si, di; Save the address of the First Equal Element
36. Sub Si, 2; as di point to the address of the next element of the equal Element
37. Lo:
38. CMP ax, ES: [di]; compare the next word
39. JNE next; if not equal goto next
40. Inc dx; if equal, increase DX
41. JMP next1; do other process
43. Next:; if not equal, mov this element to Si
44. MoV BX, ES: [di]
45. MoV ES: [Si], BX
46. Add Si, 2; change Si to the new first location
47. Next1:
48. Add Di, 2; change di to point to the next remaider Element
49. Loop Lo
51. Exit:
52. Sub ES: list [0], DX; set the new array's length
53. ; Xchg ES: list [0], DX
55. ; Display the number of the equal elements in the array
56. Add DL, 30 h
57. MoV ah, 02 h
58. Int 21 h
60. ; The exit DOS system call
61. MoV ah, 4ch
62. Int 21 h
64. Code ends
65. End start
66. .