File Io and Pass by Reference via Reference Parameters in c++ pro

Pass by Value vs. Pass by Reference

#include 

#include

using namespace std;

int inc(int number);

int main() 

{

   int n = 8;

   cout << "Before calling function, n is " << n << endl; 

   int result = inc(n);

   cout << "After calling function, n is " << n << endl;  

   cout << "Result is " << result << endl;               

}

int inc(int number) 

{

   ++number;  

   return number;

}

Pass by Reference via Reference Parameters

#include 

#include

using namespace std;

int squarebyvalue (int number);        

void squarebyreference (int & number); 

int main() 

{

   int n1 = 8;

   cout << "Before call, value is " << n1 << endl;  

   cout << squarebyvalue(n1) << endl;  

   cout << "After call, value is " << n1 << endl

   int n2 = 9;

   cout << "Before call, value is " << n2 << endl;  

   squarebyreference(n2);  

   cout << "After call, value is " << n2 << endl;   

}

int squarebyvalue (int number) 

{

   return number * number;

}

void squarebyreference (int & number) 

{

   number = number * number;

}

Test rand and srand time

#include 

#include

#include   

#include     

using namespace std;

int main() 

{

   cout << "Rand_max is " << rand_max << endl;   

   for (int i = 0; i < 10; ++i) 

   {

      cout << rand() % 100 << " ";   

   }

   cout << endl;

   srand(time(0));   

      for (int i = 0; i < 10; ++i) 

    {

      cout << rand() % 100 << " ";   

     }

   cout << endl;

}

Test rand()'s Distribution

#include 

#include

#include 

#include   

#include     

using namespace std;

const int total_count = 2000000;  

const int num_faces = 6;

int frequencies[6] = {0}; 

int main() 

{

   srand(time(0)); 

   for (int i = 0; i < total_count; ++i) 

  {

      ++frequencies[rand() % 6];

   }

   cout << fixed << setprecision(2);

   for (int i = 0; i < num_faces; i++) 

  {

      cout << i+1 << ": " << frequencies[i]

           << " (" << 100.0 * frequencies[i] / total_count << "%)" << endl;

   }

}

File IO

#include 

#include

#include   

          #include 

using namespace std;

int main() 

{

   ifstream fin;   

   ofstream fout;  

   fin.open("in.txt");

   if (!fin.is_open()) 

  {

      cerr << "error: open input file failed" << endl;

      abort();  

   }

   int sum = 0, number, count = 0;

   while (!(fin.eof())) 

  {

      fin >> number;

      sum += number;

      ++count;

   }

   double average = double(sum) / count;

   cout << "Count = " << count << " average = " << average << endl;

   fin.close();

   fout.open("out.txt");

   if (!fout.is_open()) 

   {

      cerr << "error: open output file failed" << endl;

      abort();

   }

   fout << average;

   fout.close();

   return 0;

}