Nope i don't catch it. Is that neccesary?
Yes, you DO need to catch it.
As far as I knew, a string is a array of char's. So i believe that char const*=string. Am i wrong?
A string isn't exactly a const char *. It is a class that contains a const char * and two integers that denote the size and allocated size of the array.
A const char * is just a pointer (an array, to simplify).
If you want to throw a string, you must:
throw std::string("ERROR IN NAVIGATION R1 = R2. IS v and R1 in same component");