C++ Tutorial/vector/vector indexer

Find element in a vector using a linear search

<source lang="cpp">#include <iostream>

1. include <vector>
2. include <cstdlib>
3. include <ctime>

using namespace std; int linear_search(vector<int> v, int a){

  for (int i = 0; i < v.size(); i++){  
     if (v[i] == a)
        return i;
  }
  return -1;

} void print(vector<int> a){

  for (int i = 0; i < a.size(); i++)
     cout << a[i] << " ";
  cout << "\n";

} void rand_seed(){

  int seed = static_cast<int>(time(0));
  srand(seed);

} int rand_int(int a, int b){

  return a + rand() % (b - a + 1);

} int main() {

  rand_seed();
  vector<int> v(20);
  for (int i = 0; i < v.size(); i++)
     v[i] = rand_int(1, 100);
  print(v);
  cout << "Enter number to search for: ";
  int n;
  cin >> n;
  int j = linear_search(v, n);
  cout << "Found in position " << j << "\n";
  return 0;

}</source>

Returns all values within a range

<source lang="cpp">#include <iostream>

1. include <vector>

using namespace std; vector<double> between(vector<double> v,

   double low, double high)

{

  vector<double> result;
  for (int i = 0; i < v.size(); i++)
     if (low <= v[i] && v[i] <= high)
        result.push_back(v[i]);
  return result;

} int main() {

  vector<double> salaries(5);
  salaries[0] = 35.0;
  salaries[1] = 63.0;
  salaries[2] = 48.0;
  salaries[3] = 78.0;
  salaries[4] = 51.0;
  vector<double> midrange_salaries = between(salaries, 45.0, 65.0);
  for (int i = 0; i < midrange_salaries.size(); i++)
     cout << midrange_salaries[i] << "\n";
  return 0;

}</source>

Use indexer to update element in the vector

<source lang="cpp">#include <iostream> using std::cout; using std::endl;

1. include <vector> // vector class-template definition
2. include <algorithm> // copy algorithm
3. include <iterator> // ostream_iterator iterator
4. include <stdexcept> // out_of_range exception

int main() {

  int array[ 6 ] = { 1, 2, 3, 4, 5, 6 };
  std::vector< int > integers( array, array + 6 );
  std::ostream_iterator< int > output( cout, " " );
  integers.push_back( 2 );
  integers.push_back( 3 );
  integers.push_back( 4 );
  cout << "Vector integers contains: ";
  std::copy( integers.begin(), integers.end(), output );
  integers[ 0 ] = 7; // set first element to 7
  cout << "\n\nVector integers contains: ";
  std::copy( integers.begin(), integers.end(), output );
  return 0;

}</source>

Vector integers contains: 1 2 3 4 5 6 2 3 4
Vector integers contains: 7 2 3 4 5 6 2 3 4

Use toupper function to convert all elements in a char vector to upper case

<source lang="cpp">#include <iostream>

1. include <vector>
2. include <cctype>

using namespace std; int main() {

 vector<char> v(10); // create a vector of length 10
 cout << "Size = " << v.size() << endl;
 for(int i=0; i<10; i++) 
    v[i] = i + "a";
 cout << "Current Contents:\n";
 for(int i=0; i<v.size(); i++) cout << v[i] << " ";
 cout << "\n\n";
 
 for(int i=0; i<v.size(); i++) 
    v[i] = toupper(v[i]);
 cout << "Modified Contents:\n";
 for(int i=0; i<v.size(); i++) 
    cout << v[i] << " ";
 cout << endl;
 return 0;

}</source>

Size = 10
Current Contents:
a b c d e f g h i j
Modified Contents:
A B C D E F G H I J