Code will not display getting error

I am getting an error on line 14 it will not display B. Any suggestions? This is the code:

A=[1 2 3;4 5 6;7 8 9]
[m,n]=size(A);

while j<=n
    i=1;
    sum1=0;
    while i<=m
        sum1=sum1+A(i,j);
        B(i,j)=sum1;
        i=i+1;
    end
    j=j+1;
end
disp(B)

Answer 1

[the cyclist]

I could not run your code, because j is not yet defined before you enter the loop. I initialized j to 1, and then it worked (and displayed B):

A=[1 2 3;4 5 6;7 8 9]
[m,n]=size(A);

j=1;

while j<=n
    i=1;
    sum1=0;
    while i<=m
        sum1=sum1+A(i,j);
        B(i,j)=sum1;
        i=i+1;
    end
    j=j+1;
end
disp(B)

But I don't know if that's exactly what you need.

[David Hughes]

Yes, that is what I needed. I didn't see j wasn't initialized. Thanks

Answer 2

[Steven Lord]

When you ask about an error, you should include the full, exact text of the error message rather than paraphrasing it.

But in this case, I suspect I know what's going on. What if j <= n is false when you reach your WHILE loop? The body of the WHILE loop will never execute. If B did not exist when you reach your WHILE loop, that will mean it won't exist when you try to display it. [That would mean that if j <= n was true that it was created inside the loop the first time you tried to assign into it. You should avoid doing that; search the documentation for the term "preallocation" for more information.]

[David Hughes]

ok, thanks.