Something

int     my_strlen(char *);
int     my_power_it(int nb, int power);

int     BaseToDec(char *bf,  char *nb)
{
  int   nblenght;
  int   var;
  int   decnb;

  decnb = 0;
  nblenght = my_strlen(nb);
  while (nblenght)
    {
      var = 0;
      while (bf[var] != nb[my_strlen(nb) - nblenght])
        var++;
    decnb += (var * (my_power_it(my_strlen(bf), (nblenght-- - 1))));
    }
  return (decnb);
}