[QUOTE=CRGreathouse;239167]Ah. You should only use one, but pre-set it to the appropriate size, filled with 0s, then *add* rather than concatenate. That way you can go from

[0, 0, 0, 0, 0]
to
[0, 0, 0, 0, 6]
to
[0, 0, 0, 4, 6]
to
[0, 0, 0, 13, 6]
to
[0, 0, 6, 13, 6]
which can be simplified to
[0, 0, 7, 3, 6]
and then
[7, 3, 6]
if desired.[/QUOTE]

I was thinking of using while loops and another vector, but your way works I think. The problem is if I get 9*9 then it makes it can make it even longer still.

[QUOTE=science_man_88;239206]I was thinking of using while loops and another vector, but your way works I think. The problem is if I get 9*9 then it makes it can make it even longer still.[/QUOTE]

If you multiply an n digit number by an m digit number, n + m digits will suffice (though the most significant digit may be 0).

[QUOTE=CRGreathouse;239208]If you multiply an n digit number by an m digit number, n + m digits will suffice (though the most significant digit may be 0).[/QUOTE]

Okay I think I get the preset stuff, if I just add I get 4+9+6+6 if I have it as is.

[CODE]answer[#answer-(x*y-1)]=(answer[#answer-(x*y-1)]+n);carry=floor((c[y]*d[x])/10)[/CODE]

getting closer I got to:

[CODE][6, 0, 13, 6][/CODE]

I know why it's happened, going to have to work out how to fix it. and it all has to do with: (x*y-1) because:
-(1*1-1) gives -0,
-(2*1-1) and -(1*2-1) give -1,But
-(2*2-1) gives -(3) so it skips -2 the place it should go in.

I wouldn't worry about carries; just fix them in the end.

[QUOTE=CRGreathouse;239221]I wouldn't worry about carries; just fix them in the end.[/QUOTE]

It's not a carry problem it's a placement formula error problem because I should of had a formula to place the 6 in the 2nd from right not the very right.

[QUOTE=science_man_88;239223]It's not a carry problem it's a placement formula error problem because I should of had a formula to place the 6 in the 2nd from right not the very right.[/QUOTE]

Every time you move one digit to the left on the multiplier you need to move the result one digit to the left. :smile:

[QUOTE=CRGreathouse;239229]Every time you move one digit to the left on the multiplier you need to move the result one digit to the left. :smile:[/QUOTE]

Instead of multiplying I should be adding lol and subtracting 1 I think. I'll try it.

Got it working for 2 digits I'll check for 3. If it works I'll just need to chop off a 0 on the end.

[QUOTE=science_man_88;239238]Got it working for 2 digits I'll check for 3. If it works I'll just need to chop off a 0 on the end.[/QUOTE]

oh and then the carry has to be done in the additions.

[CODE]longmultiply(a,b)= c=eval(Vec(Str(a)));d=eval(Vec(Str(b)));carry=0;answer=vector(length(d)+length(c));forstep(x=#d,1,[-1],forstep(y=#c,1,[-1],n=((c[y]*d[x])+carry)%10;answer[#answer-((#d-x+1)+(#c-y+1)-1)]=(answer[#answer-((#d-x+1)+(#c-y+1)-1)]+n);carry=floor((c[y]*d[x])/10)));forstep(w=#answer,2,-1,answer[w-1]=answer[w-1]+floor(answer[w]/10);answer[w]=answer[w]%10)[/CODE]

One thing I can't seem to do is shift it maybe I'll have to add it in as another loop, this code is making me loopy.