thank everyone for replying...
seems like it will make it difficult to convert back to decimal. so maybe its ok to display in hex...since it only take 5 bytes rather than 6 bytes with decimal..

i probably going to write in asembly since i studied about it for past few days and hardly know to write in c..

maybe i'm going to use gopal amlekar suggestion num 3 since i'm not really understand on how to work with interupt pin or counter pin...

i get the idea on scanning the port pin for pulses, but then what can i do to organize the data?

say
scan:
jnb p1.1,scan
jb p1.1,increment; detect pulse then go to increase number

how to increase the number in the memory?

so each time pulse detected, then line will add value to current value rite?

mov r1,01h
mov a,01h
add a,r1
mov r2,a

is that how to do? how to transfer for next byte?