## 8051 code to arrange the given numbers in half ascending and half descending order.

In this article let's see how to arrange a given array in half ascending and half descending. I think it's weird to hear the word half ascending and half descending but it is interesting as well.

### Algorithm:

1) Store the length of array in r5 and the memory address in r0.
2)Obtaining the half of length and store it in r3,r4,r6 because making r3 as outer counter and r6 as inner counter.
3)Compare the two numbers of an array and if the first number is lesser than second number jump to last label.
4)If the first number is greater than second number then swap the numbers stored in memory location.
5)Decrement inner counter and repeat the above 3rd and 4th step for successive numbers.
6)Decrement outer counter and repeat the above 3rd,4th and 5th steps.
7)For next half of the array repeat the same steps but check the numbers to be in descending order.

### Code goes here:

``````
org 0000h
ljmp main
org 040h
main:
mov r5,#10      ; length of array
mov a,r5
mov b,#2
div ab          ; Obtaining the half of length of array
mov r3,a
mov r4,a
mov r6,a
up1:  mov r0,#40h     ;Moving the memory address of array
mov a,r4
dec a
mov r6,a
mov b,@r0
inc r0
mov a,@r0
cjne a,b,chkasc ;Comparing which is greater
ljmp last
up:   mov b,@r0       ;Comparing the next two numbers
inc r0
mov a,@r0
cjne a,b,chkasc
ljmp last
chkasc:jnc last       ;If the two numbers are in ascending order
dec r0         ;swaping the numbers if they are greater
mov @r0,a
inc r0
mov @r0,b
last:  djnz r6,up     ;Comparing the inner counter
djnz r3,up1    ;comparing the outer counter
mov a,r5
subb a,r4
mov r3,a
mov r4,a
mov r6,a
mov r5,a
up3:   mov a,r5
mov r0,a
mov a,r4
dec a
mov r6,a
mov b,@r0
inc r0
mov a,@r0
cjne a,b,chk1   ;checking first two numbers to arrange in descending order
ljmp last1
up2:   mov b,@r0
inc r0
mov a,@r0
cjne a,b,chk1   ;checking the successive two numbers to arrange in descending order
ljmp last1
chk1:  jc last1        ; jumping if the two numbers are in descending order
dec r0          ;swaping if the first number is lesser than second number
mov @r0,a
inc r0
mov @r0,b
last1: djnz r6,up2     ;Comparing the inner counter
djnz r3,up3     ;comparing the outer counter
end

``````