Like this? i=0; while i <= 20 i = i+1; r = rem(i,3); if r == 1 disp('its first num') elseif r == 2 disp('its sec num') else disp('its 3rd num') end end

You need the == equals while(x==0 & y==0) For example: syms x y = x; f = x^2; if (limit(y,x,0)==0 & limit(f,x,0)==0) disp('true'); else disp('false'); end

You can just break the loop at that point. flags = false(1,3); while k<=y if flags(1) d(i) = 0; else d(i)=d0+((d0^2)/2)*a-((d0^2)/2)*b*w0; % a=Deer repop rate b=rate wolves find deer if d(i) < 0 flags(1) = true; end end if flags(2) m(i) = 0; else m(i)=m0+((m0^2)/2)*c-((m0^2)/2)*e*w0;% c= Moose repop rate e= rate wolves find moose if m(i) < 0 flags(2) = true; end end if flags(3) w(i) = 0; else w(i)=w0+((w0^2)/2)*f*(m0*b+d0*e)-g*w0; %f= wolves effiecency at making food into offspring g= death rate of wolves if w(i) < 0 flags(3) = true; end end d0=d(i); m0=m(i); w0=w(i); i=i+1; k=k+1; end

Doesn't this do the trick?

if yada yada
    x = f(x)   %// If you don't have anything here, you should use "if ~yada yada"
               %// instead of "else"
else
    while k>1 && x == true  %// BTW: Lower case t in true 
        x = g(y)  %// I hope you have something more than "k=k-1" in this loop
        k = k-1;
    end
end