How to do it…

Follow these steps to ensure that the pointer is not NULL and is pointing to a memory address by making use of assertions:

1. Define an array containing a number of integers whose average is to be computed:

int arr[]={3,9,1,6,2};

2. Set a pointer to point to the array:

ptr=arr; 

3. Define a function for calculating the average of the array elements. A pointer to an array and the count of the number of values in the array are both passed to this function:

average=findaverage(ptr, count); 

4. In the function, define an assert expression that ensures that the pointer is not NULL. If the pointer is NULL, the program will display an error and will be aborted:

assert(Ptr != NULL && "Pointer is not pointing to any array"); 

5. If the pointer is not NULL, the array elements will be accessed through the pointer and their average will be computed and displayed on the screen:

for(i=0;i<Count;i++)
 {
   sum+=*Ptr;
   Ptr++;
 }
Average=(float)sum/Count;

The program for implementing a validation that ensures the pointer is not NULL and is pointing to a memory address is shown as follows:

// assertprog.c
#include <stdio.h> 
#include <assert.h> 

float findaverage(int *Ptr, int Count); 

int main() 
{ 
    int arr[]={3,9,1,6,2};
    float average; 
    int *ptr=NULL,count; 
    ptr=arr; 
    count=5; 
    average=findaverage(ptr, count); 
    printf("Average of values is %f\n", average); 
    return(0); 
} 

float findaverage(int *Ptr, int Count)
{
    int sum,i;
    float Average; 
    assert(Ptr != NULL && "Pointer is not pointing to any array"); 
    sum=0; 
    for(i=0;i<Count;i++) 
    { 
        sum+=*Ptr; 
        Ptr++; 
    } 
    Average=(float)sum/Count; 
    return(Average); 
}

Now, let's go behind the scenes to understand the code better.