C++/STL Basics/array algorithms

Illustrating the generic adjacent_difference algorithm

<source lang="cpp">

1. include <iostream>
2. include <cassert>
3. include <algorithm>
4. include <numeric>

using namespace std; int main() {

 const int N = 20;
 int x1[N], x2[N];
 for (int i = 0; i < N; ++i)
   x1[i] = i;
 // Compute the partial sums of 0, 1, 2, 3, ..., N - 1, putting the result inx2:
 partial_sum(&x1[0], &x1[N], &x2[0]);
 // Compute the adjacent differences of elements in x2, placing the result back in x2:
 adjacent_difference(&x2[0], &x2[N], &x2[0]);
 for (int i = 0; i < N; ++i)
     cout << x2[i] << "  ";
 return 0;

} /* 0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19

*/        
 </source>

Illustrating the generic inner_product algorithm with predicate

<source lang="cpp">

1. include <algorithm>
2. include <iostream>
3. include <functional>
4. include <numeric>

using namespace std; int main() {

 const int N = 5;
 int x1[N], x2[N];
 for (int i = 0; i < N; ++i) {
   x1[i] = i + 1;
   x2[i] = i + 2;
 }
 
 // compute "inner product," with roles of + and * reversed:
 int result = inner_product(&x1[0], &x1[N], &x2[0], 1,multiplies<int>(), plus<int>());
 cout << "Inner product with roles of + and * reversed: " << result << endl;
 return 0;

} /* Inner product with roles of + and * reversed: 10395

*/        
 </source>

Illustrating the generic partial_sum algorithm

<source lang="cpp">

1. include <algorithm>
2. include <numeric>
3. include <iostream>

using namespace std; int main() {

 const int N = 20;
 int x1[N], x2[N];
 for (int i = 0; i < N; ++i)
   x1[i] = i;
 // Compute the partial sums of 0, 1, 2, 3, ..., N - 1, putting the result inx2:
 partial_sum(&x1[0], &x1[N], &x2[0]);
 for (int i = 0; i < N; ++i)
   cout << x2[i] << " ";
 return 0;

} /* 0 1 3 6 10 15 21 28 36 45 55 66 78 91 105 120 136 153 171 190

*/        
 </source>

Use random_shuffle algorithms with array

<source lang="cpp">

1. include <iostream>
2. include <algorithm>
3. include <cassert>
4. include <functional>

using namespace std; int main() {

 int a[100];
 int i;
 for (i = 0; i < 100; ++i) 
   a[i] = i;
 random_shuffle(&a[0], &a[100]);
 for (i = 0; i < 100; ++i) 
   cout <<  a[i] << " ";

 return 0;

} /* 12 1 9 98 96 27 58 82 86 90 18 62 32 40 71 51 91 41 94 17 8 47 64 66 65 7 6 76 5

99 77 81 54 35 56 39 25 3 87 16 61 68 14 13 24 55 97 19 20 59 75 33 21 28 78 15
50 34 36 44 83 38 46 60 84 95 57 22 37 23 70 89 31 79 73 92 11 2 88 42 30 52 72
53 67 29 85 43 74 69 45 26 93 10 48 80 0 63 49 4 "
*/        
 </source>

Use the generic partition algorithms: Partition array1, putting numbers greater than 4 first, followed by those less than or equal to 4

<source lang="cpp">

1. include <algorithm>
2. include <vector>
3. include <string>
4. include <iostream>
5. include <iterator>

using namespace std; bool above40(int n) { return (n > 4); } int main() {

 const int N = 7;
 int array0[N] = {5, 3, 1, 7, 6, 4, 2};
 int array1[N];
 copy(&array0[0], &array0[N], &array1[0]);
 ostream_iterator<int> out(cout, " ");
 cout << "Original sequence:                 ";
 copy(&array1[0], &array1[N], out); cout << endl;

 int* split = partition(&array1[0], &array1[N], above40);
 cout << "Result of (unstable) partitioning: ";
 copy(&array1[0], split, out); cout << "| ";
 copy(split, &array1[N], out); cout << endl;
 return 0;

} /* Original sequence: 5 3 1 7 6 4 2 Result of (unstable) partitioning: 5 6 7 | 1 3 4 2

*/        
 </source>

Using function templates to get the max and min value in an array

<source lang="cpp">

1. include <iostream>

using std::cout; using std::endl;

template<class T> T max(const T* data, int size) {

   T result = data[0];
   for(int i = 1 ; i < size ; i++)
     if(result < data[i])
       result = data[i];
   return result;
 }

template<class T> T min(const T* data, int size) {

   T result = data[0];
   for(int i = 1 ; i < size ; i++)
     if(result > data[i])
       result = data[i];
   return result;
 }

int main() {

 double data[] = {1.5, 4.6, 3.1, 1.1, 3.8, 2.1};
 int numbers[] = {2, 22, 4, 6, 122, 12, 1, 45};
 const int dataSize = sizeof data/sizeof data[0];
 cout << "Minimum double is " << min(data, dataSize) << endl; 
 cout << "Maximum double is " << max(data, dataSize) << endl; 
 const int numbersSize = sizeof numbers/sizeof numbers[0];
 cout << "Minimum integer is " << min(numbers, numbersSize) << endl; 
 cout << "Maximum integer is " << max(numbers, numbersSize) << endl;
 return 0;

} /* Minimum double is 1.1 Maximum double is 4.6 Minimum integer is 1 Maximum integer is 122

*/        
 </source>

Using reverse_copy to copy the array reversely

<source lang="cpp">

1. include <iostream>
2. include <algorithm>
3. include <cassert>

using namespace std; int main() {

 int a[100], b[100];
 int i;
 for (i = 0; i < 100; ++i) 
   a[i] = i;
 reverse_copy(&a[0], &a[100], &b[0]);

 for (i = 0; i < 100; ++i) 
    cout << " a: "<< a[i] << "b: " <<  b[i] << " \n";
 return 0;

} /*

a: 0b: 99
a: 1b: 98
a: 2b: 97
a: 3b: 96
a: 4b: 95
a: 5b: 94
a: 6b: 93
a: 7b: 92
a: 8b: 91
a: 9b: 90
a: 10b: 89
a: 11b: 88
a: 12b: 87
a: 13b: 86
a: 14b: 85
a: 15b: 84
a: 16b: 83
a: 17b: 82
a: 18b: 81
a: 19b: 80
a: 20b: 79
a: 21b: 78
a: 22b: 77
a: 23b: 76
a: 24b: 75
a: 25b: 74
a: 26b: 73
a: 27b: 72
a: 28b: 71
a: 29b: 70
a: 30b: 69
a: 31b: 68
a: 32b: 67
a: 33b: 66
a: 34b: 65
a: 35b: 64
a: 36b: 63
a: 37b: 62
a: 38b: 61
a: 39b: 60
a: 40b: 59
a: 41b: 58
a: 42b: 57
a: 43b: 56
a: 44b: 55
a: 45b: 54
a: 46b: 53
a: 47b: 52
a: 48b: 51
a: 49b: 50
a: 50b: 49
a: 51b: 48
a: 52b: 47
a: 53b: 46
a: 54b: 45
a: 55b: 44
a: 56b: 43
a: 57b: 42
a: 58b: 41
a: 59b: 40
a: 60b: 39
a: 61b: 38
a: 62b: 37
a: 63b: 36
a: 64b: 35
a: 65b: 34
a: 66b: 33
a: 67b: 32
a: 68b: 31
a: 69b: 30
a: 70b: 29
a: 71b: 28
a: 72b: 27
a: 73b: 26
a: 74b: 25
a: 75b: 24
a: 76b: 23
a: 77b: 22
a: 78b: 21
a: 79b: 20
a: 80b: 19
a: 81b: 18
a: 82b: 17
a: 83b: 16
a: 84b: 15
a: 85b: 14
a: 86b: 13
a: 87b: 12
a: 88b: 11
a: 89b: 10
a: 90b: 9
a: 91b: 8
a: 92b: 7
a: 93b: 6
a: 94b: 5
a: 95b: 4
a: 96b: 3
a: 97b: 2
a: 98b: 1
a: 99b: 0
*/        
 </source>

Using the STL generic reverse algorithm with an array

<source lang="cpp">

1. include <iostream>
2. include <string>
3. include <cassert>
4. include <algorithm> // For reverse algorithm

using namespace std; int main() {

 char array1[] = "abc";
 int N1 = strlen(array1);
 reverse(&array1[0], &array1[N1]);
 assert (string(array1) == "cba");
 return 0;

}

 </source>