UVa 1586 - Molar mass

Accepted date: 2015-01-05
Language: C++

/*
  UVa 1586 - Molar mass

  To build using Visual Studio 2012:
    cl -EHsc -O2 UVa_1586_Molar_mass.cpp
*/

#include <cstdio>
#include <cstdlib>

int main()
{
  const int nr_chars_max = 80;
  const double w_carbon = 12.01,  w_hydrogen = 1.008, w_oxygen = 16.00,
    w_nitrogen = 14.01;
  int T;
  scanf("%d", &T);
  while (T--) {
    char s[nr_chars_max + 1];
    scanf("%s", s);
    int carbon = 0, hydrogen = 0, oxygen = 0, nitrogen = 0;
    for (char* p = s; *p; ) {
      char* pe = p + 1;
      if (*p == 'C' || *p == 'H' || *p == 'O' || *p == 'N') {
        int n = strtol(p + 1, &pe, 10);
        if (!n)
          n = 1;
        switch (*p) {
        case 'C':
          carbon += n; break;
        case 'H':
          hydrogen += n; break;
        case 'O':
          oxygen += n; break;
        case 'N':
          nitrogen += n; break;
        }
      }
      p = pe;
    }
    double w = w_carbon * carbon + w_hydrogen * hydrogen + w_oxygen * oxygen +
      w_nitrogen * nitrogen;
    printf("%.3lf\n", w);
  }
  return 0;
}