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# Passing pointers to functions in C++

C++ allows you to pass a pointer to a function. To do so, simply declare the function parameter as a pointer type.

Following a simple example where we pass an unsigned long pointer to a function and change the value inside the function which reflects back in the calling function:

    #include <iostream>
    #include <ctime>

    using namespace std;
    void getSeconds(unsigned long *par);

    int main ()
    {
       unsigned long sec;

       getSeconds( &sec );

       // print the actual value
       cout << "Number of seconds :" << sec << endl;

       return 0;
    }

    void getSeconds(unsigned long *par)
    {
       // get the current number of seconds
       *par = time( NULL );
       return;
    }

When the above code is compiled and executed, it produces following result:

    Number of seconds :1294450468

The function which can accept a pointer, can also accept an array as shown in the following example:

    #include <iostream>
    using namespace std;

    // function declaration:
    double getAverage(int *arr, int size);

    int main ()
    {
       // an int array with 5 elements.
       int balance[5] = {1000, 2, 3, 17, 50};
       double avg;

       // pass pointer to the array as an argument.
       avg = getAverage( balance, 5 ) ;

       // output the returned value
       cout << "Average value is: " << avg << endl;

       return 0;
    }

    double getAverage(int *arr, int size)
    {
      int    i, sum = 0;
      double avg;

      for (i = 0; i < size; ++i)
      {
        sum += arr[i];
       }

      avg = double(sum) / size;

      return avg;
    }

When the above code is compiled together and executed, it produces following result:

    Average value is: 214.4

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