signed fields

[dummies2]

i have this chart :

A                 1
B                 2
C                 3
D                 4 
E                 5
F                 6
G                 7
H                 8
I                  9
J                  0

and

K                 -1
L                 -2
M                -3
N                -4
O                -5
P                -6
Q               -7
R                -8
S                -9
T                -0

so for example if i have a number like this.
12.89 then i need to convert it to :

+12.89 = 128I
-12.89 = 128S

-0.19 = 01S
+0.19 = 01I

that is what i have to do. now i could just write crazy if and else if statment for each number from 1 to 0 with plus and minus sign to do this, but is there easier way and faster too? ty. as of this moment i couldnt think of any. plz help me guys