Compiler says cast then when done says no can do

[Ty Tower]

I have this line

double balance=values[6]-values[5]; (values 5&6 are char[])

so I change to 
double balance=-(double)values[6]-(double)values[5]; 
compiler says : C style cast illegal, use cast(double)values[6]

so I change to 
double balance=cast(double)values[6]-cast(double)values[5]; 
compiler says: Error: e2ir: cannot cast from char[] to double

So as I see it the compiler message in this case at least is wrong or there is a problem casting from a char array to a double . Is it a problem with the compiler message?