Example of Self modifying ASM code :P

[dragonboy269]

Here's a simple code that modifies one of its instructions when certain conditions are met. (like changing an add instruction to a subtract)
I dunno I was just bored XD

Press L+R to add to your bells if less than 99,900. If it is more than 99,900, it'll start subtracting instead, until it reaches 100 or less. It'll keep going back and forth :P

023FF090 012FFF11
E0000000 00000040
E28F2001 E12FFF12
8800480A 01122230
D10D4210 68214C08
42A94D08 2339DB01
2964E002 2331DC02
7053A200 60213164
00004770 04000130
021D891C 0001863C
023FF090 E3520003

ASM source:

@convert to thumb
add r2,pc,#1
bx r2
.thumb

ldr r0, IOKeys
ldrh r0, [r0]

@Activate if L+R pressed
mov r2, #0x30
lsl r2, #0x4
tst r0, r2
bne Exit

ldr r4, Bell_Amount
ldr r1, [r4]
ldr r5, TestAmount

@Check if bells 99,900 or more
cmp r1, r5
blt CheckZero

@#0x39 is value for sub r1
mov r3, #0x39
b StoreInstruction

@check if bells 100 or less
CheckZero:
cmp r1, #100
bgt AddOrSubtract

@#0x31 is value for add r1
mov r3, #0x31

StoreInstruction:

@store instruction
adr r2, AddOrSubtract
strb r3, [r2, #1]

AddOrSubtract:
add r1, #100
str r1, [r4]
Exit:
bx lr

.arm
IOKeys:
.long 0x4000130
Bell_Amount:
.long 0x21D891C
TestAmount:
.long 0x1863C

It works a lot easier in ARM mode, but...it's just an example.