Printing arrays elements in reverse order using pointer-CodePudding

I am trying to input an array and then print it in reverse order using for loop. Firstly, I tried to print out the array elements in original order as follows:

#include <stdio.h>

int main()
{
    int a[100];
    int n,i;
    int *p=a;
    printf("Enter size of array:");
    scanf("%d",&n);
    printf("Enter array elements:");
    for(i=0;i<n;i  ){
        printf("Enter array element [%d]:",i);
        scanf("%d",p i);
    }
    printf("Array elements in reverse order: ");
    for (i=0;i<n;i  ){
        printf("%d\n",*(p i));
    }

The above code worked and desired output was achieved. And then I tried to output array elements in reverse order using following changes in the last for loop:

for (i=n;i>0;i--){
    printf("%d\n",*(p i));

But doing this the output appears as below:

while the desired output is:

3
2
1

What am I missing?

CodePudding user response：

In your first attempt, the indices range from 0 to n-1 which is correct. In your second attempt the indices range from n to 1, so you read and write one element past the end of the array.

The proper initialization and condition is:

for (i=n-1;i>=0;i--){

CodePudding user response：

You iterate from p 3 (array[3]), while max index is 2 -> undefined behavior, garbage printed

You iterate until p 0, excluded, you exclude array[0].

for (i = n - 1; i >= 0; i--) {
  //... 
}