Programs Involving Searching for a string,palindrome

1. Write an ALP to search a character in a string.

2.Write an ALP to given string is palindrome or not.

 1.Write an ALP to search a character in a string.

CODE:

data SEGMENT 

 MSG1 DB 10,13,'ENTER THE STRING:$'     ; Message to prompt for string input

 MSG2 DB 10,13,'Exists$'                ; Message to indicate the character exists

 MSG3 DB 10,13,'Does not exist$'        ; Message to indicate the character does not exist

 MSG4 DB 10,13,'ENTER THE Character:$'  ; Message to prompt for character input

 STR1 DB 50 DUP(0)                      ; String input buffer, 50 bytes initialized to 0

data ENDS

code SEGMENT

ASSUME CS:code, DS:data  

START:

    MOV AX, data

    MOV DS, AX                      ; Initialize data segment

    LEA DX, MSG1

    MOV AH, 09H

    INT 21H                         ; Display "ENTER THE STRING:"

    LEA DI, STR1                    ; Point DI to the string buffer

    MOV AH, 01H                     ; Prepare to read a character

NEXT_CHAR:

    INT 21H                         ; Read a character

    CMP AL, 0DH                     ; Check if the character is Carriage Return (Enter key)

    JE TERMINATE                    ; If Enter, terminate input

    MOV [DI], AL                    ; Store the character in the buffer

    INC DI                          ; Increment DI to next position

    JMP NEXT_CHAR                   ; Continue reading characters

TERMINATE: 

    MOV AL, '$'                     ; Terminate the string with a '$'

    MOV [DI], AL

     

    LEA DX, MSG4

    MOV AH, 09H

    INT 21H                         ; Display "ENTER THE Character:"

    MOV AH, 01H

    INT 21H                         ; Read the character to search for

    MOV BL, AL                      ; Store the character in BL

    LEA SI, STR1                    ; Point SI to the start of the string

    MOV CX, 50                      ; Set CX to the maximum string length (50)

CHECK_CHAR:

    LODSB                           ; Load byte from string into AL and increment SI

    CMP AL, '$'                     ; Check if end of string

    JE NOTEXISTS                    ; If end of string, character not found

    CMP AL, BL                      ; Compare string character with the search character

    JE EXISTS                       ; If found, jump to EXISTS

    LOOP CHECK_CHAR                 ; Repeat for the length of the string

NOTEXISTS:

    LEA DX, MSG3

    MOV AH, 09H

    INT 21H                         ; Display "Does not exist"

    JMP END_PROGRAM

EXISTS:

    LEA DX, MSG2

    MOV AH, 09H

    INT 21H                         ; Display "Exists"

END_PROGRAM:

    MOV AH, 4CH

    INT 21H                         ; Terminate program

code ENDS

END START

OUTPUT:

                     

EXPLAINATION:

I'd be glad to explain the assembly code you provided:

Data Segment:

• data SEGMENT: This line defines a segment in memory named "data". Segments are used to organize different parts of a program.
• Message Variables (MSG1, MSG2, MSG3, MSG4):
  • DB (Define Byte): These lines define byte arrays to store string messages displayed to the user.
  • 10, 13: These are the ASCII codes for newline (\n) and carriage return (\r), respectively, used for formatting the output.
  • The messages prompt the user for input and indicate the search results.
• STR1 DB 50 DUP(0): This line defines a byte array named STR1 with 50 bytes (enough to hold up to 49 characters plus the null terminator). DUP(0) initializes all bytes to 0, creating an empty string buffer.

Code Segment:

• code SEGMENT: This line defines the code segment where the program instructions reside.
• ASSUME CS:code, DS:data: These lines inform the assembler about the segment registers used for code (CS) and data (DS).
• START:: This label marks the beginning of the program's execution.
• MOV AX, data: This instruction loads the address of the "data" segment into the AX register.
• MOV DS, AX: This instruction sets the DS register (data segment) to the value in AX, initializing the data segment for accessing variables.
• Displaying "ENTER THE STRING:" (Lines starting with LEA DX and ending with INT 21H):
  • LEA DX, MSG1**: This instruction loads the address of the MSG1 message into the DX register for displaying.
  • MOV AH, 09H**: This sets the AH register (interrupt service routine function number) to 9, which is the DOS function for displaying a string.
  • INT 21H**: This instruction triggers an interrupt (a signal to the operating system) with number 21H, invoking the DOS function to display the string.

Reading Input String:

• LEA DI, STR1: This instruction loads the address of STR1 into the DI register, pointing it to the start of the string buffer.
• MOV AH, 01H: This sets AH to 1, which is the DOS function number for reading a character from the keyboard.
• NEXT_CHAR: This label marks the loop for reading characters.
  • INT 21H: This interrupts the CPU to read a character.
  • CMP AL, 0DH: This instruction compares the character in AL (register holding the read character) with the ASCII code for \r (carriage return).
  • JE TERMINATE: If AL is equal to 0DH (Enter key pressed), jump to the TERMINATE label to end input.
  • MOV [DI], AL: This instruction stores the read character into the current position of the string buffer pointed to by DI.
  • INC DI: This increments DI to point to the next byte in the buffer for the next character.
  • JMP NEXT_CHAR: This instruction jumps back to the NEXT_CHAR label, continuing the character reading loop.

Terminating String Input:

• TERMINATE:: This label marks the termination point for string input.
• MOV AL, '$': This loads the dollar sign ($) character into AL, which acts as the string terminator.
• MOV [DI], AL: This stores the $ character at the end of the string buffer.

Searching for a Character:

• Displaying "ENTER THE Character:" (Repeated Lines): This part is identical to the previous message display functionality.
• MOV AH, 01H: This sets AH for reading a character to search for.
• INT 21H: This reads the search character from the keyboard.
• MOV BL, AL: This stores the read character in the BL register for comparison.
• LEA SI, STR1: This loads the address of STR1 into SI, pointing it to the beginning of the string.
• MOV CX, 50: This sets CX 

Searching for a Character 

• CHECK_CHAR:: This label marks the loop for checking characters in the string.
  • LODSB: This instruction loads a byte from the memory location pointed to by SI into AL and increments SI automatically. This effectively moves SI through the string while loading each character into AL for comparison.
  • CMP AL, '$': This compares the character in AL with the dollar sign ($), the string terminator.
  • JE NOTEXISTS: If AL is equal to $ (end of string reached), jump to the NOTEXISTS label, indicating the character wasn't found.
  • CMP AL, BL: This compares the character in AL with the search character in BL.
  • JE EXISTS: If AL is equal to BL (character found), jump to the EXISTS label.
  • LOOP CHECK_CHAR: This instruction decrements CX by 1. If CX is not zero, it jumps back to the CHECK_CHAR label, continuing the loop for the remaining characters in the string.

Displaying Search Results:

• NOTEXISTS:: This label marks the point where the character wasn't found.

• LEA DX, MSG3: This loads the address of the message "Does not exist" into DX for display.

• MOV AH, 09H: This sets AH for displaying a string.

• INT 21H: This calls the DOS function to display "Does not exist".

• JMP END_PROGRAM: This unconditional jump transfers control to the program termination part.

• EXISTS:: This label marks the point where the character was found.

• LEA DX, MSG2: This loads the address of the message "Exists" into DX for display.

• MOV AH, 09H: This sets AH for displaying a string.

• INT 21H: This calls the DOS function to display "Exists".

Program Termination:

• END_PROGRAM:: This label marks the program's end.
• MOV AH, 4CH: This sets AH to 4CH, which is the DOS function number for program termination.
• INT 21H: This triggers the interrupt with 21H, calling the DOS function to terminate the program.
• code ENDS: This marks the end of the code segment.
• END START: This signifies the overall program end, with START being the starting point.

In summary, this assembly code prompts the user to enter a string and a character, then searches for the character within the string. It displays messages indicating whether the character was found or not.

2.Write an ALP to given string is palindrome or not.

code:

.model small

.stack 100h

data SEGMENT

    MSG1 DB 10,13,'ENTER THE STRING: $'

    MSG2 DB 10,13,'STRING IS PALINDROME$'

    MSG3 DB 10,13,'STRING IS NOT PALINDROME$'

    STR1 DB 50 DUP(0)

data ENDS

code SEGMENT

ASSUME CS:code, DS:data

START:

    ; Initialize Data Segment

    MOV AX, @data

    MOV DS, AX

    

    ; Display message to enter the string

    LEA DX, MSG1

    MOV AH, 09H

    INT 21H  

    

    LEA SI,STR1

    LEA DI,STR1

    

    MOV AH,01H

NEXT:

    INT 21H

    CMP AL,0DH

    JE TERMINATE

    MOV [DI],AL

    INC DI

    JMP NEXT

TERMINATE:

    MOV AL,'$'

    MOV [DI],AL    

   

DOTHIS:

    ; Compare characters from both ends

    DEC DI

    MOV AL, [SI]  

    

    CMP [DI],AL

    JNE NOTPALINDROME

    

    ; Move pointers

    INC SI

    CMP SI,DI

    JL DOTHIS

    ; If palindrome, display message

    PALINDROME:

        MOV AH, 09H

        LEA DX, MSG2

        INT 21H

        JMP XX

NOTPALINDROME:

    ; If not palindrome, display message

    MOV AH, 09H

    LEA DX, MSG3

    INT 21H

XX:

    ; Exit program

    MOV AH, 4CH

    INT 21H

code ENDS

END START

OUTPUT:

EXPLAINATION:

Explanation of the Assembly Code for Palindrome Checking

This assembly code checks if a user-entered string is a palindrome. Here's a breakdown of each section:

Model and Stack:

• .model small: This line defines the memory model for the program. small indicates a 16-bit memory model with limited addressing capabilities.
• .stack 100h: This allocates 100h (256 bytes) of memory for the program's stack, used for storing temporary data during function calls.

Data Segment:

• data SEGMENT: This marks the beginning of the data segment. It holds static data like messages and the string buffer.
  • Message variables (MSG1, MSG2, MSG3):
    • DB (Define Byte): These lines define byte arrays for string messages displayed to the user.
    • 10, 13: These represent the ASCII codes for newline (\n) and carriage return (\r), respectively, used for formatting the output.
    • The messages prompt the user for input and indicate the palindrome result.
  • STR1 DB 50 DUP(0): This defines a byte array named STR1 with 50 bytes (enough to hold up to 49 characters plus the null terminator). DUP(0) initializes all bytes to 0, creating an empty string buffer.
• data ENDS: This marks the end of the data segment.

Code Segment:

• code SEGMENT: This marks the beginning of the code segment. It holds the program instructions.
• ASSUME CS:code, DS:data: These lines inform the assembler about the segment registers used for code (CS) and data (DS).
• START:: This label marks the program's entry point.

Initialization:

• MOV AX, @data: This loads the address of the "data" segment into the AX register. The @ symbol is used to get the segment address.
• MOV DS, AX: This sets the DS register (data segment) to the value in AX, initializing the data segment for accessing variables.

Prompting and Reading Input:

• Displaying "ENTER THE STRING:" (Lines starting with LEA DX and ending with INT 21H):

  • LEA DX, MSG1**: This loads the address of the MSG1 message into the DX register for displaying.
  • MOV AH, 09H**: This sets AH (interrupt service routine function number) to 9, which is the DOS function for displaying a string.
  • INT 21H**: This triggers an interrupt (a signal to the operating system) with number 21H, invoking the DOS function to display the string.

• LEA SI, STR1: This instruction loads the address of STR1 into the SI register, pointing it to the start of the string buffer.

• LEA DI, STR1: This loads the address of STR1 into the DI register, pointing it to the beginning of the buffer as well.

• MOV AH, 01H: This sets AH to 1, which is the DOS function number for reading a character from the keyboard.

• NEXT: This label marks the loop for reading characters.

  • INT 21H: This instructs the operating system to read a character.
  • CMP AL, 0DH: This compares the character in AL (register holding the read character) with the ASCII code for \r (carriage return).
  • JE TERMINATE: If AL is equal to 0DH (Enter key pressed), jump to the TERMINATE label to end input.
  • MOV [DI], AL: This stores the read character into the current position of the string buffer pointed to by DI.
  • INC DI: This increments DI to point to the next byte in the buffer for the next character.
  • JMP NEXT: This jumps back to the NEXT label, continuing the character reading loop.

Terminating String Input and Adding Null Terminator:

• TERMINATE:: This label marks the termination point for string input.
  • MOV AL, '$': This loads the dollar sign ($) character into AL, which acts as the string terminator.
  • MOV [DI], AL: This stores the $ character at the end of the string buffer.

Palindrome Check:

• DOTHIS:: This label marks the loop for checking if the string is a palindrome.
  • DEC DI: This decreases DI to point to the character just before the $ (excluding the terminator).
  • MOV AL, [SI]: This loads the character at the current position pointed to by SI into the AL register.
• CMP [DI], AL: This compares the character in AL with the character pointed to by DI.
  • JNE NOTPALINDROME: If the characters are not equal, jump to the NOTPALINDROME label, indicating the string is not a palindrome.
• Moving Pointers and Checking for Midpoint:
  • INC SI: This increments SI to point to the next character towards the center of the string.
  • CMP SI, DI: This compares SI and DI.
  • JL DOTHIS: If SI is less than DI (pointers haven't met in the middle yet), jump back to DOTHIS to continue checking characters.

Displaying Results:

• PALINDROME:: This label marks the point where the loop finishes without encountering mismatching characters (palindrome).
  • MOV AH, 09H: This sets AH for displaying a string.
  • LEA DX, MSG2: This loads the address of the "STRING IS PALINDROME" message into DX.
  • INT 21H: This calls the DOS function to display the message.
• NOTPALINDROME:: This label marks the point where a mismatch was found (not a palindrome).
  • MOV AH, 09H: This sets AH for displaying a string.
  • LEA DX, MSG3: This loads the address of the "STRING IS NOT PALINDROME" message into DX.
  • INT 21H: This calls the DOS function to display the message.

Program Termination:

• XX:: This label marks the program's end point.
  • MOV AH, 4CH: This sets AH to 4CH, which is the DOS function number for program termination.
  • INT 21H: This terminates the program by calling the DOS function.
• code ENDS: This marks the end of the code segment.
• END START: This signifies the overall program end, with START being the starting point.

This code effectively reads a string from the user, checks if it's a palindrome, and displays the appropriate message.