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Passing pointers to functions in C
C programming allows passing a pointer to a function. To do so, simply declare the function parameter as a pointer type.
Following is 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 <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
The function, which can accept a pointer, can also accept an array as shown in the following example −
#include <stdio.h> /* 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 */ 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 together and executed, it produces the following result −
Average value is: 214.40000
c_pointers.htm
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