1: //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 sort() "
39: "algorithm (extended version)\nto sort a vector of integers, "
40: "when a first integer comes before a second if and\nonly if "
41: "the first has a smaller digit sum than the second.";
42: cout << "\nPress Enter to continue ... "; cin.ignore(80, '\n');
44: int a[] = {17, 12, 14, 19, 23, 15, 61, 20, 81, 11};
45: vector<int> v(a, a+10);
47: cout << "\nHere are the original contents of the vector:\n";
48: for (vector<int>::size_type i=0; i<v.size(); i++)
49: cout << v.at(i) << " ";;
50: cout << "\nPress Enter to continue ... "; cin.ignore(80, '\n');
52: sort(v.begin(), v.end(), hasSmallerDigitSum);
54: cout << "\nAnd here the sorted contents of the vector:\n";
55: for (vector<int>::size_type i=0; i<v.size(); i++)
56: cout << v.at(i) << " ";;
57: cout << "\nPress Enter to continue ... "; cin.ignore(80, '\n');
58: }