c++ - Error in my programming code -

i first course in programming c++, , don't know why program doesn't work correctly. able me? there way know how many loop round did before loop stops (that is, when p = 0 in case)?

#include <iostream>  using namespace std;   int main() {     float p, i, m;      cout << " indiquer le montant du prêt($), le taux d'intérêt par an(%), et le payement mensuel($) :";     cin >> p >> >> m;          {         float * s;          s = &(p*i/12*100);          cout << p-(m-s);       } while (p != 0)        return 0;  } 

when using do...while loop, while should end ';'.

do  {     float  s;      s = (p*i/12*100);      cout << p-(m-s);   } while (p != 0); 

and ignore pointers, because there no need of it...