How to store a string of numbers sequentially?

I am attempting to analyze a string such as "20times30", storing 20 in one memory or register location, then 30 in an alternate memory location. I am able to do it with single digit integers such as "2times3" however, I am unsure as to storing more than 1 digit sequentially.

I have tried storing the first digit into a memory location, then looping and shifting the store location to store the second digit. The issue is that it creates 0x00000002 and 0x00000002 for example in memory rather than 22.

   AREA Lab6, CODE, READONLY
ENTRY
 LDR r0,=ASCII_STRING ;Load ASCII string into r0 for processing  
 LDR r2,=operand_1  ;Create essentially a variable that the numbers can be stored to
 LDR r3,=operand_2 ; Load an inititial value of 0 into register 3
 MOV r5,#0x0
 MOV r6,#0x0
numbers
    LDRB r1,[r0]
    CMP r1,'9'
    BHI letters
    CMP r1,'0'
    BLS stop
    BHI convertnumbers
    CMP r1,'G'
    BEQ stop
letters
    CMP r1,'t'
    MOVEQ r4,'t'
    ADDEQ r0,#5
    BEQ numbers2
    CMP r1,'a'
    MOVEQ r4,'a'
    ADDEQ r0,#3
    BEQ numbers2
    BNE stop

convertnumbers
    SUB r1,r1,#0x30
    STRB r1,[r2,r5]
    ADD r5,r5,#1
    B numbers   

numbers2
    LDRB r1,[r0]
    CMP r1,'9'
    BHI letters
    CMP r1,'0'
    BLS stop
    BHI convertnumbers2
    CMP r1,'G'
    BEQ stop
convertnumbers2
    SUB r1,r1,#0x30
    STRB r1,[r3,r5]
    ADD r6,r6,#1
    B numbers


stop b stop


    AREA asciiCode, DATA, READONLY
ASCII_STRING  DCB "2times3",'G'  ;ASCII code string
    AREA binary_form, DATA, READWRITE
operand_1  SPACE 20   ;area to store converted binary string
operand_2 SPACE 20 ; op2

   END

The memory value at the effective address of operand_1 should be 22 rather than 02 02. I realize the loop currently infinitely stores 02 into the memory; however, I believe I can fix that.