I am working on ROT13 program with linux.

I have to use I/O such as Stdin and Stdout, so i am using Read and write.

The code in the Read section as below

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mov eax,3

mov ebx, 0

mov ecx,Buff

mov edx,1

int 80h

cmp eax,0

je,exit

cmp byte[Buff],41h

jb Write

cmp byte [Buff],7Ah

ja Write

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I don't know how to compare the upper case letters and lower case letters seperately.

For example, if i put "Hello. My name is Bob.", i have to get "Uryyb. Zl anzr vf Obo."

Please help me out.