Program 6: Finding Prime Numbers in a Range

 **Program 6: Finding Prime Numbers in a Range**

```assembly

.model small

.stack 100h

.data

    start dw 1

    end dw 20

.code

    main proc

        mov ax, start           ; Load 'start' into AX

        

    find_primes:

        inc ax                  ; Move to the next number

        cmp ax, end             ; Compare with 'end'

        jg end_prog             ; Jump to end if AX > 'end'

        

        mov cx, ax              ; Copy AX to CX

        mov bx, 2               ; Divisor

        

    check_prime:

        xor dx, dx              ; Clear DX for division

        div bx                  ; Divide CX by BX

        cmp dx, 0               ; Check remainder

        je not_prime            ; If remainder = 0, not prime

        inc bx                  ; Move to next divisor

        cmp bx, cx              ; Compare divisor with CX

        jg prime                ; If divisor > CX, number is prime

        jmp check_prime         ; Otherwise, continue loop

        

    not_prime:

        jmp find_primes         ; Check next number

        

    prime:

        ; Print prime number in AX

        mov ah, 02h             ; DOS function to print character

        add al, 30h             ; Convert number to ASCII

        mov dl, al              ; Load ASCII character

        int 21h                 ; Print character

        

        jmp find_primes         ; Check next number

        

    end_prog:

        mov ah, 4Ch             ; Exit program

        int 21h

    main endp

end main

```

Explanation:

1. `.model small` and `.stack 100h`: Memory model and stack size definitions.

2. `.data` section: Declares the data segment.

   - `start dw 1`: Defines a word-sized variable named "start" with value 1.

   - `end dw 20`: Defines a word-sized variable named "end" with value 20.

3. `.code` section: Contains the main code.

   - `mov ax, start`: Move the value of "start" into the AX register.

   - `find_primes:`: Label for the loop.

   - `inc ax`: Increment AX to the next number.

   - `cmp ax, end`: Compare AX with "end".

   - `jg end_prog`: Jump to the end if AX > "end".

   - `mov cx, ax`: Copy AX to CX (number to be checked for prime).

   - `mov bx, 2`: Initialize the divisor to 2.

   - `check_prime:`: Label for the divisor checking loop.

   - `xor dx, dx`: Clear DX for division.

   - `div bx`: Divide CX by BX (quotient in AX, remainder in DX).

   - `cmp dx, 0`: Check if remainder is 0.

   - `je not_prime`: Jump to "not_prime" if remainder is 0 (not prime).

   - `inc bx`: Move to the next divisor.

   - `cmp bx, cx`: Compare divisor with CX.

   - `jg prime`: If divisor > CX, the number is prime.

   - `jmp check_prime`: Otherwise, continue the divisor loop.

   - `not_prime:`: Label for when the number is not prime.

   - `jmp find_primes`: Check the next number.

   - `prime:`: Label for when the number is prime.

   - `mov ah, 02h`: DOS function to print character.

   - `add al, 30h`: Convert the number to ASCII.

   - `mov dl, al`: Load the ASCII character to print.

   - `int 21h`: Print the character.

   - `jmp find_primes`: Check the next number.

   - `end_prog:`: Label for the end of the program.

   - `mov ah, 4Ch`: Set the exit code for DOS.

   - `int 21h`: Call DOS interrupt to exit the program.