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Passing Pointers to Functions in C

C Pointers

C allows you to pass pointers to functions by simply declaring the function parameters as pointer types.

In the following example, we pass an unsigned long pointer to a function and change its value within the function:

Example

#include <stdio.h>
#include <time.h>

void getSeconds(unsigned long *par);

int main ()
{
   unsigned long sec;

   getSeconds( &sec );

   /* Print the actual value */
   printf("Number of seconds: %ld\n", sec );

   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 the following result:

Number of seconds: 1294450468

Functions that can accept pointers as parameters can also accept arrays as parameters, as shown below:

Example

#include <stdio.h>

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

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

   /* Pass a pointer to the array as an argument */
   avg = getAverage( balance, 5 ) ;

   /* Print the returned value */
   printf("Average value is: %f\n", avg );

   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 and executed, it produces the following result:

Average value is: 214.400000

C Pointers

❮ C Nested Loops C Function Ldiv ❯