log and rand() gives not a number

In the following part of code:

I want to generate a random number "U" from the range 0 to 1, then I calculate an equation having log

The error is: some value of U makes the log in the equation give "not a number"value

I tried casting the "U" to float or double or even round it to 2 decimal places but same error

vector <double>Xs;//random Xs
double x;
double U;

   while (check_arr < 360)
    {

        U = ((rand() / RAND_MAX) * 100) / 100;
        x = (log10(1 - U)) / (-1 / a);
        Xs.push_back(x);

    }