How to split text box input value

i need help from u all
example:

i will enter text box 145
i don't enter , or :,"",, nothing


i want split this number into sprat

s1=1
s1=4
s1=5
what i want to
than mach with this each number to this charter
this is i will set default
1=s1
srt="R"
2=s1
str="W"
3=s1
str="Y"
4=s1
str="M"
5=s1
str="L"


else
str1=X
output come like as RML
if will enter number 44
now output come like MX
send some idea and sample

help me

thank u