syms h q x f(x) f0 f1(x) f2(x) f3(x)
f = f0 + f1*q + f2*q.^2 + f3*q.^3;
Eq0 = diff(f,x) - diff(f0,x);
Eq1 = diff(f,x) - f^2;
A = (1-q)*(Eq0) == h*q*Eq1;
B = diff(A,q);
C = subs(B,[q,f0],[0,1])
As stated on its doc page, int() does not return a constant of integration in its result, so it has to be added explicitly:
syms C1
D = int(lhs(C),x) == int(rhs(C),x) + C1
