Compare char in Micro ASM 1.00

Question

How to compare two char, the first one is user input.

include 'emu8086.inc'

#make_COM#

ORG 100h

answer DW ?
score DW ?

MOV score, 0

PRINT "This is a 10 question Exam"

PUTC 13
PUTC 10
PUTC 13
PUTC 10

PRINT "1.) A is the Answer"
PUTC 13
PUTC 10
PRINT " A.)"
PUTC 13
PUTC 10
PRINT " B.)"
PUTC 13
PUTC 10
PRINT " C.)"
PUTC 13
PUTC 10
PRINT " D.)"
PUTC 13
PUTC 10
PRINT "Your Answer: "  
LEA     DI, buffer      
MOV     DX, 10     
CALL GET_STRING  
MOV answer, AX
PUTC 13
PUTC 10

MOV     SI, answer
CALL    print_string

CMP SI, answer
JE Correct
JMP result

Correct:
ADD score, 1
JMP result

result: 
PRINT "Your Score: "
CALL PRINT_NUM

RET

buffer DB "x"

DEFINE_SCAN_NUM
DEFINE_PRINT_NUM
DEFINE_PRINT_NUM_UNS
DEFINE_PRINT_STRING
DEFINE_GET_STRING

END

Answer 1

buffer DB "x"

This will not give you enough buffer space! If you stick with your definition of mov dx, 10 then you need to change this into: buffer db "1234567890". Since as I will explain 2 bytes will be enough this can become buffer db "12"

LEA     DI, buffer
MOV     DX, 10
CALL GET_STRING
MOV answer, AX

You don't seem to know how the GET_STRING procedure works! It stores your input zero-terminated in the DX bytes buffer at DS:DI. Since your answer will be a single character, you need to define DX=2 and you can retrieve the answer through mov ax, [di] mov answer, ax. Hereafter answer is a zero-terminated string having a single character for its contents.

MOV     SI, answer
CALL    print_string

Here you moved the contents of answer in SI. You need the address of a zero-terminated string to be passed to the PRINT_STRING procedure, so write: lea si, answer call PRINT_STRING

CMP SI, answer
JE Correct
JMP result

Because of how you setup SI this compare will always return Correct. You have to compare the contents with a defined value: mov al, [si] cmp al, "A"(Hint: you wrote "A is the Answer")