Source of partial_sort2a.cpp

Structures and functions

  1: //partial_sort2a.cpp

  3: #include <iostream>
  4: #include <vector>
  5: #include <algorithm>
  6: using namespace std;

  8: /**
  9: Tests if one integer has a smaller digit sum than another.
 10: Pre:\n i1 and i2 have been initialized and i1, i2 are both > 0.
 11: Post:\n Returns true if sum of the digits in i1 is < sum of digits
 12: in i2, and otherwise returns false.
 13: */
 14: bool hasSmallerDigitSum
 15: (
 16:     int i1, //in
 17:     int i2  //in
 18: )
 19: {
 20:     int digitSum1 = 0;
 21:     while (i1 != 0)
 22:     {
 23:         digitSum1 += i1 % 10;
 24:         i1 /= 10;
 25:     }

 27:     int digitSum2 = 0;
 28:     while (i2 != 0)
 29:     {
 30:         digitSum2 += i2 % 10;
 31:         i2 /= 10;
 32:     }
 33:     return digitSum1 < digitSum2;
 34: }

 36: int main()
 37: {
 38:     cout << "\nThis program illustrates the use of the STL "
 39:         "partial_sort() algorithm (extended\nversion) to partially "
 40:         "order a vector of integers of size 12 by moving the first"
 41:         "\n5 values in the given ordering to the beginning of the "
 42:         "vector, in the proper\norder. The range of values following "
 43:         "this value may also be ordered, but the\nalgorithm does not "
 44:         "guarantee this, and you should not expect it. In this case"
 45:         "\nthe order of the elements is determined by one integer "
 46:         "preceding another if\nand only if it has a smaller digit sum.";
 47:     cout << "\nPress Enter to continue ... ";  cin.ignore(80, '\n');

 49:     int a[] = {92,  21,  53, 84,  46,  13, 41, 76,  45,  61,  11,  15};
 50:     vector<int> v(a, a+12);
 51:     cout << "\nHere are the initial contents of the vector:\n";
 52:     for (vector<int>::size_type i=0; i<v.size(); i++)
 53:         cout << v.at(i) << " ";
 54:     cout << "\nPress Enter to continue ... "; cin.ignore(80, '\n');

 56:     cout << "\nNow we make the following call:";
 57:     cout << "\npartial_sort(v.begin(), v.begin()+5, "
 58:         "v.end(), hasSmallerDigitSum);";
 59:     partial_sort(v.begin(), v.begin()+5, v.end(), hasSmallerDigitSum);
 60:     cout << "\nPress Enter to continue ... "; cin.ignore(80, '\n');

 62:     cout << "\nAnd here are the (partially sorted) contents of the "
 63:         "vector,\nup to and including its 7th element:\n";
 64:     for (vector<int>::size_type i=0; i<v.size(); i++)
 65:         cout << v.at(i) << " ";
 66:     cout << "\nPress Enter to continue ... "; cin.ignore(80, '\n');
 67: }