.data
        prompt_str: .ascii "Input a string of up to 32 chars long: \000"
        result_str: .ascii "Result is: %s\n\000"
        exit_str: .ascii "Exiting...\n\000"
        fmt_str: .asciz "%[^\n]%*c"
        input_str: .ascii

.text
.global main
.extern printf scanf

main:
        push {ip,lr}
        mov r4,#0
start:
        ldr r0, =prompt_str
        bl printf

        ldr r0, =fmt_str
        ldr r1, =input_str
        bl scanf

        ldr r0, =input_str
        mov r2,r0

        ldrb r1,[r0,#+1]
        cmp r1,#0
        bne transform

        ldrb r1,[r0]
        cmp r1,#'Q'
        beq exit
        cmp r1,#'q'
        beq exit
transform:
        mov r3,#0
loop:
        cmp r3,#32
        strgeb r4,[r0],#1
        bge print
        add r3,r3,#1
        # manipulate each byte of the input string
        ldrb r1,[r0],#1
        # check if string is terminated with \000

        cmp r1,#'0'
        blt loop

        cmp r1,#'4'
        # if number ['0'-'4'] then add 5
        addle r1,r1,#5
        ble change

        cmp r1,#'9'
        # if number ['5'-'9'] then subtract 5
        suble r1,r1,#5
        ble change

        cmp r1,#'A'
        blt loop

        cmp r1,#'Z'
        # convert to lowercase
        suble r1,r1,#('A' - 'a')
        ble change

        cmp r1,#'a'
        blt loop

        cmp r1,#'z'
        # convert to uppercase
        suble r1,r1,#('a' - 'A')

change:
        # store transformed byte
        strb r1,[r0,#-1]
        b loop
print:
        mov r0,r2
        ldr r0, =result_str
        ldr r1, =input_str
        bl printf
        b start

exit:
        ldr r0,=exit_str
        bl printf
        pop {ip,pc}

.end