How does the code work?

Hi guys, I am learning on how to use MATLAB and currently im learning about making a user defined function for the Simpson's rule. The following is the code that I am looking at from the textbook "Numerical Methods for Engineers and Scientists":

function [ s ] = test( FunName,a,b)

N=2;
h=(b-a)/N;
x=a:h:b;
y=FunName(x);
MaxTol=1.0;
I1=h/3*(y(1)+4*sum(y(2:2:N))+2*sum(y(3:2:(N-1)))+y(N+1));
N=2*N;
check=0;

while check==0;
    h=(b-a)/N;
    x=a:h:b;
    y=FunName(x);
    I2=h/3*(y(1)+4*sum(y(2:2:N))+2*sum(y(3:2:(N-1)))+y(N+1));
    CurTol=abs(I1-I2)/I1*100;
    
    if CurTol>MaxTol
        check=0;
        N=N*2;
        I1=I2;
    elseif CurTol<=MaxTol
        check=1;
        I1=I2;
    end
end


disp(I1)
end

Now i just want to ask on what 'check' does in this code? Presumably that 'check' here tells MATLAB to continually iterate but I dont understand how it stops it. Thanks in advance

[David Hill]

check is a flag that continues the while loop until it changes to 1 in the elseif statement.

[Faris Sulam]

So because the code has set that check has to only run when it equals to 0, when the else if condition is fulfilled, check =1 and that discontinues the iterations?

[David Hill]

yes

[Faris Sulam]

Thanks