Write program by For loop, how can I stop

Hi guys, I have a program, I use for loop, the answer is right , but I want to stop on the first negative answer. This is my program

A=[40 47 50 60 70 75 80 80 90 55];
B(1)=70;
C(1)=60;
for k=1:9;
    C(k+1)= B(k)+C(k)-A(k);
    B(k+1)= A(k);
    if C(k+1)>=40
        B(k+1)=0
        k=k+1
    end   

end

C=C

The answer is 60 90 43 -7 -17 -27 -32 -37 -37 -47

How can I stop the answer on -7

Thank you

Answer 1

[Matt Fig]

A=[40 47 50 60 70 75 80 80 90 55];
B(1)=70;
C(1)=60;
for k=1:9;
    C(k+1)= B(k)+C(k)-A(k);
    if C(k+1)<0,break,end  % Stops the loop.
    B(k+1)= A(k);
    if C(k+1)>=40
        B(k+1)=0
        k=k+1
    end   

end

[sss dzu]

thank you Matt. Awesome