Inline asm and c array questions - c++

Question

This is a homework. I have 3 arrays, v1={5,4,3,2,1} ,v2={1,2,3,4,5} and v3={2,3,5,1,4}, the assigment is to change the 1 to 6. Of course, any solution like v1[4]=6, in asm or c is forbidden. So this was my code:
First Code
void main(){
int myArray[5]={5,4,3,2,1};
__asm {
mov ecx,0 //using ecx as counter
myLoop:
mov eax, myArray[ecx] //moving the content on myArray in position ecx to eax
cmp eax,1 //comparing eax to 1
je is_one //if its equal jump to label is_one
inc ecx //ecx+1
cmp ecx,5 //since all vectors have size 5, comparing if ecx is equal to 5
jne myLoop //if not, repeat
jmp Done //if true, go to label Done
is_one:
mov myArray[ecx],6 //changing the content in myArray position ecx to 6
inc ecx //ecx+1
cmp ecx,5 // ecx=5?
jne myLoop //no? repeat loop
jmp Done //yes? Done
Done:
}
printArray(myArray);
}
this didn't work, tried many things like mov eax,6 or mov [eax+ecx],6 , nothing worked until I found this solution
Many tries later code
void main(){
int myArray[5]={5,4,3,2,1};
__asm {
mov ecx,0 //using ecx as counter
myLoop:
mov eax, myArray[TYPE myArray*ecx] //I don't understand how this works
cmp eax,1 //comparing eax to 1
je is_one //if its equal jump to label is_one
inc ecx //ecx+1
cmp ecx,5 //since all vectors have size 5, comparing if ecx is equal to 5
jne myLoop //if not, repeat
jmp Done //if true, go to label Done
is_one:
mov myArray[TYPE myArray*ecx],6 //Uhh...
inc ecx //ecx+1
cmp ecx,5 // ecx=5?
jne myLoop //no? repeat loop
jmp Done //yes? Done
Done:
}
printArray(myArray);
}
And that works like a charm. But I don't understand how or why the MOV array[TYPE array * index], value works(besides TYPE returning the size as explained in link), and why not the others.
Also, since I have to do this for 3 arrays, I tried to copy and paste all the code to changingArray(int myArray[]), declared the 3 arrays in the main, and passed them to changingArray, but now is not changing them. Im pretty sure that with vector you dont have to pass with &, I could be wrong. Still, I can't see why it doesn't change them. So...
Final Code
void changingArray(int myArray[]){
__asm {
mov ecx,0 //using ecx as counter
myLoop:
mov eax, myArray[TYPE myArray*ecx] //I don't understand how this works
cmp eax,1 //comparing eax to 1
je is_one //if its equal jump to label is_one
inc ecx //ecx+1
cmp ecx,5 //since all vectors have size 5, comparing if ecx is equal to 5
jne myLoop //if not, repeat
jmp Done //if true, go to label Done
is_one:
mov myArray[TYPE myArray*ecx],6 //Uhh...
inc ecx //ecx+1
cmp ecx,5 // ecx=5?
jne myLoop //no? repeat loop
jmp Done //yes? Done
Done:
}
printArray(myArray);
}
void main(){
//for some odd reason, they arent changing
int v1[5]={5,4,3,2,1};
int v2[5]={1,2,3,4,5};
int v3[5]={2,3,5,1,4};
changingArray(v1);
changingArray(v2);
changingArray(v3);
}
TL:DR section:
Homework of changing the number 1 to 6 in 3 arrays v1={5,4,3,2,1} ,v2={1,2,3,4,5} and v3={2,3,5,1,4}
1-I don't get why the first code doesn't work, but many tries later code works (the MOV array[TYPE array * index], value instruction).
2- Since I need to do this with 3 arrays, I put all the code in changingArray(int myArray[]), and in the main I declared my 3 arrays in main as shown in final code. While many tries code did change the array, this doesnt. Probably I just made a mistake in c and not asm, but I don't see it.
And sorry for bad english, is not my first language.

Answer 1

mov eax, myArray[TYPE myArray*ecx]
Here the address referred to is (base address of myArray) + sizeof(the type of elements of myArray) * ecx. In assembly language the indexing should be done in bytes.