Weird lost of variable c++

Question

I am trying to translate a code from matlab to c++. But i've experienced serious problems with that. Today i am looking for help about a error in which i assing a value for a variable i use it without redefining but when i verify its value has change. It goes:
double dt = 3e-14;
double verif = dt; //here is ok
while (En_k[i] <=100){
trace[i] = trace[i-1] + v*dt + a/2*dt^2;
vel=vel + a*dt;
En_k[i+1] = ...
time[i+1] = time[i] + dt;
//but when i verify dt
if (verif !=dt){ cout << "error";} \\happens

Answer 1

Please refer:

https://stackoverflow.com/questions/590822/dealing-with-accuracy-problems-in-floating-point-numbers

As to why strict equality should not be used to evaluate float/double values, and how to overcome the issue.

Answer 2

@Raúl Moreno

If that is the case, we may need to inspect the entire code.

Answer 3

to extend my explanation when i do:
double dt =3e-14;
double verif=dt;
cout<< verif; // prints 3 e-14
//but after operations
cout << verif; // prints something diferent, example 35358