Switch Case Implementation, Easiest Implementation, Choice Assembly Language, ASM, MASM, NASM Switch CASE

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;Programmed by SAQIB KHAN ;Purpose: Obtain Choice from user/Implement case ;Dated: 15th-MAY-2012 .model small .stack 100h .data num1 db 97 num2 db 2 msg_add db 10, "Press 0 for Addition $" msg_sub db 10, "Press 1 for Subtraction $" msg_adc db 10, "Press 2 to add with carry $" message db 10, "Enter your choice: $" msg_wrong db 10, "Please enter correct choice $" msg_verify db 10, "First operand sholud be greater than 2nd,Please change input values $" .code main: mov ax,@data mov ds,ax lea dx,msg_add ;Display add message mov ah,9h int 21h lea dx,msg_sub ;Display subtract message mov ah,9h int 21h lea dx,msg_adc ;Display add message mov ah,9h int 21h lea dx,message ;Display choice message mov ah,9h int 21h ;;;;;;;;;;;;;;;;;;;; mov ah,1 ;read key from user int 21h mov ah,0 ;empty the ah ,upper part of ax sub al,30h ; subtract 30h to get exact value from ascii shl al,1 ; multiply number by 2 to get to the case cmp al,4 ;compare for validity jg check ;jump if al,greater than 4 mov bx,ax ;mov value of ax to bx for offset jmp cs:jmptble [bx] ;jumptable jmptble dw case0,case1,case2 ;cases check: lea dx,msg_wrong ;Display wrong choice mov ah,9h int 21h mov dl,10 ;Move to new line mov ah,2h int 21h jmp main ;Loop again to get correct choice case0: ;Case0- Addition mov dl,10 ;move to new line mov ah,2h int 21h mov al,num1 ;copy num1 to al xor ah,ah ;empty ah to zero add al,num2 ; add num2 to al call display jmp endlabel ;jum to endlabel case1: ;Case1 for subtraction mov dl,10 ;;Move to new line mov ah,2h int 21h mov cl,num1 ;Copy number1 to cl cmp cl,num2 ;check if first numbr is smaller than second jl verify ;jump if num1 is less than num2 mov al,num1 ;copy num1 to al xor ah,ah ;empty the uper portion of ax sub al,num2 ;subtract two nmbers call display jmp endlabel case2: mov dl,10 mov ah,2h int 21h mov al,num1 xor ah,ah adc al,num2 ;adc add 1 value to the sum (if carry flag is 1) call display jmp endlabel verify: lea dx,msg_verify mov ah,9 int 21h display: mov dl,10 ;mov dl,10 to divide result in ax div dl ;Dvide ax by 10 mov dl,al ;copy quotient to dl mov bl,ah ;copy remainder to bl add dl,30h ;add 30h to get actual number mov ah,2h ;Service # to display character int 21h ;Call OS to do the job add bl,30h ;add 30h to remainder mov dl,bl ;move to dl to display mov ah,2h ;Service # to display character int 21h ;Call OS to do the job ret endlabel: mov ah,4ch int 21h end main