--- title: "8086 ALP: display only alphabetic characters" subject: "Microprocessor" chapter: 3 key: "semester_4/microprocessor:alp-8086-alphabetic-only" source: https://www.bctengineer.com/q/semester_4/microprocessor/alp-8086-alphabetic-only site: BCT Engineering --- # 8086 ALP: display only alphabetic characters Microprocessor · Chapter 3: Programming with 8086 Microprocessor - Asked in: 2071 Magh, 8 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_4/microprocessor/alp-8086-alphabetic-only - Whole chapter: https://www.bctengineer.com/md/semester_4/microprocessor/chapter-3 ## Question Write a program to read a string and display only the alphabetic characters from the string in a clear screen. ## Short answer Read the string with function 0Ah and clear the screen. Classify each character: return 1 for vowel, 2 for consonant, 0 for non-letter. Only display characters whose classification is nonzero using function 02h, so digits, spaces and symbols are skipped. Example: B.C.T 2079! outputs BCT. ## Answer **Method:** read the string, clear the screen and examine each character with `CLASSIFY` (it returns 0 for non-letters, 1 for vowels and 2 for consonants). Only characters with AL ≠ 0 are displayed, so digits, spaces and symbols are dropped. ```asm .MODEL SMALL .STACK 100H DISPSTR MACRO MSG ; display a '$'-terminated string LEA DX,MSG MOV AH,09H INT 21H ENDM CLRSCR MACRO ; clear screen and home the cursor MOV AX,0600H ; scroll whole window (AL=0 -> blank it) MOV BH,07H ; normal attribute MOV CX,0000H ; upper-left corner (row 0, col 0) MOV DX,184FH ; lower-right corner (row 24, col 79) INT 10H MOV AH,02H ; set cursor position MOV BH,00H ; page 0 MOV DX,0000H ; row 0, col 0 INT 10H ENDM .DATA MSG1 DB 'Enter a string: $' BUF DB 80, ?, 80 DUP(0) ; DOS buffered-input area (max, actual, chars) CRLF DB 13,10,'$' .CODE MAIN PROC MOV AX,@DATA MOV DS,AX DISPSTR MSG1 ; prompt LEA DX,BUF ; read the string with DOS function 0Ah MOV AH,0AH INT 21H CLRSCR LEA SI,BUF+2 MOV CL,BUF+1 MOV CH,0 JCXZ EXIT NEXT: MOV DL,[SI] CALL CLASSIFY ; AL = 0 -> not a letter CMP AL,0 JE SKIP MOV AH,02H ; letter -> display it INT 21H SKIP: INC SI LOOP NEXT EXIT: MOV AH,4CH ; return to DOS INT 21H MAIN ENDP ; ---- classify the character in DL ; returns AL = 1 vowel, 2 consonant, 0 not a letter (DL unchanged) CLASSIFY PROC MOV AL,DL OR AL,20H ; fold to lower case (valid for letters) CMP AL,'a' JB NOTLET CMP AL,'z' JA NOTLET CMP AL,'a' JE VOW CMP AL,'e' JE VOW CMP AL,'i' JE VOW CMP AL,'o' JE VOW CMP AL,'u' JE VOW MOV AL,2 ; consonant RET VOW:MOV AL,1 ; vowel RET NOTLET:MOV AL,0 ; not a letter RET CLASSIFY ENDP END MAIN ``` **Example:** input `B.C.T 2079!` → output `BCT`. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which characters are displayed? A. Only vowels B. Those for which CLASSIFY returns a non-zero value C. Those for which CLASSIFY returns 0 D. All characters except spaces Answer: B. CLASSIFY returns 0 only for non-letters, so non-zero means a letter. (Key point: Filter rule) 2. What happens to digits, spaces and symbols? A. They are shown as blanks B. They are converted to letters C. They are shown at the end D. They are skipped without display Answer: D. When AL = 0 the program jumps to SKIP and moves to the next character. (Key point: Dropped characters) 3. What is displayed for input B.C.T 2079! ? A. B.C.T B. BCT C. BCT 2079 D. B C T Answer: B. Only the letters B, C and T are alphabetic. (Key point: Example) 4. What is done between reading the string and displaying letters? A. The string is sorted B. Digits are converted C. The screen is cleared D. The string is reversed Answer: C. The program calls CLRSCR after input so only the alphabetic output is visible. (Key point: Sequence) ## Related in Microprocessor - [8086 ALP: count vowels and display string](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Aalp-8086-count-vowels-display) — Microprocessor, chapter 3 - [8086 ALP: alternate case display](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Aalp-8086-alternate-case) — Microprocessor, chapter 3 - [8086 ALP: largest and smallest, display](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Aalp-8086-largest-smallest-display) — Microprocessor, chapter 3 - [8086 ALP: count vowels, consonants, numerals](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Aalp-8086-count-vowels-consonants-numerals) — Microprocessor, chapter 3 - [8086 ALP: words on separate lines, centered](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Aalp-8086-words-separate-lines-center) — Microprocessor, chapter 3 - [8086 ALP: words on lines and word count](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Aalp-8086-words-lines-count) — Microprocessor, chapter 3 ## Related in other subjects - [Rewrite string characters alphabetically](https://www.bctengineer.com/question.md?key=semester_1%2Fcomputer_programming%3Astring-alphabetical-order) — Computer Programming, chapter 7 - [Display N characters using default arguments](https://www.bctengineer.com/question.md?key=semester_3%2Fobject_oriented_programming%3An-chars-default-args-program) — Object Oriented Programming, chapter 3 - [Display characters between given ranges](https://www.bctengineer.com/question.md?key=semester_1%2Fcomputer_programming%3Acharacters-between-ranges) — Computer Programming, chapter 5 - [Check string consists of alphabet only](https://www.bctengineer.com/question.md?key=semester_1%2Fcomputer_programming%3Astring-alphabet-check) — Computer Programming, chapter 7