Assembly CMP and JNZ

This is the second type of use CMP with comparison. JNZ is a command that tell the program to jump is comparison result is not equal. If equal, please don't jump.

start:

    MOV AH,08    ; Function to read char from keyboard

    INT 21h      ; and save it to AL

    CMP AL,65    ; Compare what valu in AL to "A"

    JNZ output   ; if not same (not zero), please jump and 

                 ; skip middle. If zero, please run code normally

middle:

    MOV AH,02    ; Function to output char

    MOV DL,"R"   ; Char to output

    INT 21h

output:

    MOV AH,02    ; Function to output char

    MOV DL,"T"   ; Char to output

    INT 21h

exit:

   MOV AH,4Ch    ; Exit function

   MOV AL,00     ; Return 0

   INT 21h

 
If you type "A", it means that the comparison is same, and the command is JUMP IF NOT EQUAL, so the result is that the code will executed normally:

output> RT

But if you type other than "A", it means that the comparison result is not equal to zero (not same), and the command is JUMP IF NOT EQUAL, so the result is that the program will jump to output and skip middle label:
output> T

Assembly CMP and JNZ