How to draw a vector in 3D?

Hello everyone, I'm doing a math project and there is a problem that I want to ask you. The project require to enter a coordinate of a point M. This point M belongs to the region limited by planes: z=4-y^2,z=0,x=0,x=1 and then draw the vector of this field in the position of M.

I try this code but it didn't work:

syms x y z
disp('Enter the coordinate of M');
x0=input('x0=');
y0=input('y0=');
z0=input('z0=');
g1=z+y^2-4;
g2=x-1;
g3=x;
g4=z;
if (z0~=4-y0^2) && (x0~=0) && (x0~=1) && (z0~=0) 
    disp('Nhap lai toa do M');
    return
end
if (z0==4-y0^2) 
    quiver3(x0,y0,z0,double(subs(diff(g1,x),x0)), double(subs(diff(g1,y),y0)), double(subs(diff(g1,z),z0)));
else if (x0-1==0)
        quiver3(x0,y0,z0,double(subs(diff(g2,x),x0)), double(subs(diff(g2,y),y0)), double(subs(diff(g2,z),z0)));
    else if (x0==0)
          quiver3(x0,y0,z0,double(subs(diff(g3,x),x0)), double(subs(diff(g3,y),y0)), double(subs(diff(g3,z),z0)));
        else if (z0==0)
                quiver3(x0,y0,z0,double(subs(diff(g4,x),x0)), double(subs(diff(g4,y),y0)), double(subs(diff(g4,z),z0)));
            end 
        end
    end
end

Please help me to fix it. Your help will be really appreciated. Thank you so much!