Operation on Strings in Assembly Language

Algorithm for Operation on Strings

Step I    :    Initialize the data and stack memory.
Step II    :    Using Macro display Menu.
        1.    Accept
        2.    Length
        3.    Reverse
        4.    Palindrome
        5.    Exit.
Step III    :    Accept choice from user using INT 21H, function 01H.
Step IV    :    IS choice = 1  jump to step XI else goto step V.
Step V    :    IS choice = 2 jump to step XIV else goto step VI.
Step VI    :    IS choice = 3 jump to step XVII else goto step VII.
Step VII    :    IS choice = 4 jump to step XX else goto step VIII.
Step VIII    :    IS choice = 5 jump to step XXIII else goto step IX.
Step IX    :    Display Wrong choice.
Step X    :    Jump to step II.
Step XI    :    Call procedure accept.
Step XII    :    Accept string using INT 21H, function 0AH.
Step XIII    :    Return to main program and goto step II.
Step XIV    :    Call procedure length.
Step XV    :    Calculate the length of string and display it using INT 21H, function 02H.
Step XVI    :    Return back to main program and jump to step II.
Step XVII    :    Call procedure reverse.
Step XVIII    :    Reverse the string and display it.
Step XIX    :    Return back to main program and jump to step II.
Step XX    :    Call procedure palindrome.
Step XXI    :    Check if string is palindrome. If yes display string is palindrome else string is not a palindrome.
Step XXII    :        Return back to main program and jump to step II.
Step XXIII    :    Terminate the program and stop.

 TITLE  STRING OPERATIONS  
 MESS  MACRO MSG     ; DEFINITION OF MACRO MESS         
      MOV      AH, 09H  
      LEA      DX, MSG  
      INT      21H  
      ENDM  
 .MODEL SMALL   
 .STACK 100H  
 .DATA  
      STR1      DB 25 , ? , 25 DUP('$')   
      STR3      DB 25 , ? , 25 DUP('$')   
      MSG1      DB 0AH, 0DH, 'MENU $'  
      MSG21      DB 0AH, 0DH, '1.ACCEPT $'  
      MSG22      DB 0AH, 0DH, '2.LENGTH $'  
      MSG23      DB 0AH, 0DH, '3.REVERSE $'  
      MSG24      DB 0AH, 0DH, '4.PALINDROME $'  
      MSG25      DB 0AH, 0DH, '5.EXIT $'  
      MSG3      DB 0AH, 0DH, 'ENTER YOUR CHOICE : $'  
      MSG4      DB 0AH, 0DH, 'WRONG CHOICE $'  
      MSG5      DB 0AH, 0DH, 'ENTER THE STRING : $'  
      MSG6      DB 0AH, 0DH, 'STRING IS : $'  
      MSG7      DB 0AH, 0DH, 'LENGTH IS : $'  
      MSG8      DB 0AH, 0DH, 'THE STRING IS A PALINDROME  $'  
      MSG9      DB 0AH, 0DH, 'THE STRING IS NOT A PALINDROME  $'  
 .CODE   
 mov     ax,           @data     ; Intialize data and extra segment  
      mov           ds, ax  
      mov           es, ax  
 ak :     mess           msg1     ; display menu  
      mess           msg21  
      mess           msg22  
      mess           msg23  
      mess           msg24  
      mess           msg25  
      mess           msg3     ; accept choice  
      mov           ah, 01h  
      int           21h  
      mov           bl, al     ; Choice BL  
      cmp          bl, 31h     ; if choice=1  
      je           acc          ; Accept string  
      cmp           bl, 32h     ; if choice=2  
      je           len          ; Find lenth   
                                    ; of string  
      cmp           bl, 33h     ; if choice=3  
      je           rev          ; Reverse string  
      cmp           bl, 34h     ; if choice=4  
      je           pal          ; Check if string is   
                                    ; palindrome  
      cmp           bl, 35h     ; if choice=5  
      je           endd     ; exit  
      mess           msg4     ; Wrong Choice  
      jmp           ak  
 acc :     call           accept  
      jmp           ak  
 len :     call           lent  
      jmp           ak  
 rev :     call           reverse  
      jmp           ak  
 pal:     call           pall  
      jmp           ak  
 endd:     mov           ah, 4ch  
      int           21h  
 ;      accept      procedure                                            
      accept proc near  
      mess      msg5  
      mov      ah, 0ah     ; Accept String  
      lea           dx, str1  
      int           21h  
      RET  
 accept endp  
 ; length procedure    
 lent proc near     
      mess           msg7   
      mov           dl, str1+1     ; Dl contains length of String  
      or           dl, 30h  
      mov           ah, 02h          ; Display Length                           
      int           21h  
      ret   
 lent endp  
 ; reverse procedure    
 reverse proc near  
      mess           msg6  
      mov           ch, 00h  
      mov           cl, str1+1     ; Cl has length of string  
      sub           cl, 01h  
      lea           si, str1+2     ; DESTINATION STRING  
      lea           di, str1+2     ; DESTINATION STRING  
      repz           movsb          ; COPY TO TRAVERSE TILL END OF FIRST STR  
      mov           cl, str1+1         
      lea           di, str3+2     ; DESTINATION STRING  
 loop1:      mov           dx, [si]          ; dx contains rightmost character  
      mov           ah, 02h  
      int           21h          ; display character  
      mov           [di], dx          ; copy character to destination  
      dec           si  
      inc           di  
      dec           cl  
      cmp           cl, 00h  
      jne           loop1  
      ret  
 reverse endp  
 ; palindrome procedure    
 pall      proc           near  
      mess           msg6  
      mov           ah, 09h  
      lea           dx, str1+2     ; str1 contains original string  
      int           21h  
      call           reverse               ; str3 has reversed string   
      lea           di, str3+2  
      mov           ah, 00h  
      mov           dh, 00h  
      lea           si , str1+2  
      mov           cl, str1+1          ; CL contains Length of string  
 loop 2 :     mov           al, byte ptr[si]  
      mov           bl, byte ptr[di]  
      dec           cl                    ; Decrement count  
      cmp           cl, 00h  
      je           loopa  
      cmp           al, bl               ; Compare characters  
      je           loop3               ; if same goto loop3  
 loopa : cmp           cl, 00h               ; if checked all characters  
      je           loop4  
      mess           msg9               ; the strings are not same  
      jmp           loop5  
 loop4 : mess           msg8               ; the strings are same  
 loop5: ret  
 loop3 : inc           si  
      inc           di  
      jmp           loop2               ; now check next character  
      pall           endp  
 end

How to Run this Program 

For Running this program you should have installed Tasm on you computer . If you have not installed Tasm  yet please install from Here .