codewars #include's the different files together, essentially just concatenating them. So you're causing conflicts by adding the entire std namespace into the main file.

You can still have that using directive inside your function.

when i try to use (using namespace std;) i couden't ATTEMPT it

random_tests
testing_toIndustrial_for_random_int_inputs
testing_toIndustrial_for_random_string_inputs
testing_toNormal_for_random_double_inputs
Expected: equal to 0.77
Actual: 0.78

toNormal_for_random_double_inputs has a string output!!