Sample sources.

1 Hello World.cpp

// Just printing a message.

#include <iostream>
using namespace std;

int main() {
  cout << "Hello" << " " << "world";
  cout << "Hello world";
  return 0;
}

2 Modulo.cpp

// Demonstration of modulo capabilities.

#include <iostream>
using namespace std;

int main() {
  int a, b;
  a = 10;
  b = 7;
  cout << a / b << endl;
  cout << a % b << endl;
  return 0;
}

3 Clock.cpp

// Popping next hour on a 12-hour clock.

#include <iostream>
using namespace std;

int main() {
  int a;
  cin >> a;
  a = a - 1;
  a = a + 1;
  a = a % 12;
  a = a + 1;
  cout << a << endl;
  return 0;
}

4 Bills Naive.cpp

// Paying with a minimum amount of bills.

#include <iostream>
using namespace std;

int main() {
  int bills[] = { 200, 100, 50, 20, 10, 5, 2, 1 }, n, i;
  i = 0;
  cin >> n;
  while (n != 0) {
    while (bills[i] > n) {
      i = i + 1;
    }
    cout << bills[i] << ' ';
    n = n - bills[i];
  }
  return 0;
}

5 Bills Counter Test.cpp

// This one shows why the naive approach is wrong.

#include <iostream>
using namespace std;

int main() {
  int bills[] = { 5, 4, 1 }, n, i;
  cin >> n;
  while (n != 0) {
    i = 0;
    while (bills[i] > n) {
      i = i + 1;
    }
    cout << bills[i] << ' ';
    n = n - bills[i];
  }
  return 0;
}

6 Sequence Sum.cpp

// Program for calculating the sum of an integer sequence.

#include <iostream>
using namespace std;

int main() {
  int marks[10], n, i, sum;
  
  // Reading stuff.
  cin >> n;
  i = 0;
  while (i < n) {
    cin >> marks[i];
    i = i + 1;
  }
  
  // Summing up.
  sum = 0;
  i = 0;
  while (i < n) {
    sum = sum + marks[i];
    i = i + 1;
  }
  
  cout << sum;
  return 0;
}

7 Digit Sum.cpp

// It figurs out the sum of digits.

#include <iostream>
using namespace std;

int main() {
  int kriakoziabra, sum;
  sum = 0;
  cin >> kriakoziabra;
  while (kriakoziabra != 0) {
    sum = sum + kriakoziabra % 10; // Retrieving the last digit.
    kriakoziabra = kriakoziabra / 10; // Chopping it off.
  }
  cout << sum; // Voila!
  return 0;
}