find_max.asm

finds the maximum between numbers

.data
MSG1 db 'Please enter up to 20 valid single-digit positive numbers or press enter', 10, 13, '$'
MSG2 db 'Invalid number, please retry', 10, 13, '$'
MSG3 db 'max = ', '$'
array db 20 dup(?)

.stack
'stack' dw 100h dup(?)         ;256 word stack

.code
      MOV AX, @data             ;initializing
      MOV DS, AX

      CALL INPUT                ;call to input process
      CALL FINDMAX              ;call to findmax process
      CALL OUTPUT               ;call to output process

      MOV AH, 4CH               ;ending program
      INT 21H

      INPUT PROC                ;procedure for input
      MOV CX, 20                ;initializing counter for 20 repetitions
      MOV SI, 0                 ;initializing pointer array

      LEA DX, MSG1              ;printing first message
      MOV AH, 09
      INT 21H

REPEAT: MOV AH, 01H            ;reading input from keyboard
        INT 21H

        CMP AL, 13             ;check if enter
        JE ENDPROC             ;if enter, no more input

        CMP AL, '0'            ;check if valid number
        JB ERROR
        CMP AL, '9'            ;check if valid number
        JA ERROR

        MOV ARRAY[SI], AL      ;moving number to memory
        INC SI                 ;incrementing pointer
        LOOP REPEAT            ;next iteration

        JMP ENDPROC

ERROR:  LEA DX, MSG2           ;printing error message
        MOV AH, 09
        INT 21H

        JMP REPEAT             ;reading number again, counter and pointer NOT changed

ENDPROC: RET                    ;end or procedure, back to main program
        INPUT ENDP

        FINDMAX PROC           ;procedure for finding maximum
        MOV CX, SI             ;the number of iteration is the number SI reached before enter
        MOV SI, 0              ;need to reinitialize pointer
        MOV AL, ARRAY		;moving first number to al, use as current maximum
COMPLOOP: CMP ARRAY[SI], AL    ;comparing AL with every value of array, AL holds current maximum
          JB SKIP
          MOV AL, ARRAY[SI]    ;new current maximum moved to AL
SKIP:   INC SI                 ;incrementing pointer
        LOOP COMPLOOP          ;next check

        RET                    ;end of procedure, back to main program
        FINDMAX ENDP

        OUTPUT PROC
        PUSH AX                ;pushing contents of AX to save them from interrupt corruption
        LEA DX, MSG3           ;printing third message
        MOV AH, 09
        INT 21H

        POP AX                 ;restoring AX
        MOV DL, AL             ;moving number to dl to print
        MOV AH, 02             ;printing number
        INT 21H

        RET                    ;end of procedure, back to main program
        OUTPUT ENDP