invalid type argument of '->' (have 'struct arr')

Question

#include<stdio.h>
#include<stdlib.h>

struct arr{
    int *temp;
    int size;
}*var;

void inputArray(int);
void displayArray(int);

int main()
{

    int cases,i;
    printf("Enter the no of test cases\n");
    scanf("%d",&cases);
    for(i=0;i<cases;++i)
    {
        printf("Entering test case %d:\n\n",i+1);
        inputArray(i);
    }
    printf("You have entered the following\n");
    for(i=0;i<cases;++i)
    {
        printf("Test case %d\n\n",i+1);
        displayArray(i);
    }
    return 0;
}

void inputArray(int count)
{
    int i;
    printf("Enter the size of the array\n");
    scanf("%d",&(var+count)->size);
    (var+count)->temp=(int*)malloc(sizeof(int)*(var+count)->size);
    if((var+count)->temp==NULL)
    {
        printf("NOT ENOUGH MEMORY IN HEAP");
        exit(1);
    }
    printf("Enter the array\n");
    for(i=0;i<(var+count)->size;++i)
    {
        scanf("%d", &(var+count)->temp[i] );
    }

}

void displayArray(int count)
{
    int i;
    printf("\n");
    for(i=0;i<(var+count)->size;++i)
    {
        printf(" %d ",(var+count)->temp[i]);
    }
    printf("\n");
}

In the above code, whenever I replace (var+count)->... with var[count]-> it shows the error :" invalid type argument of '->' (have 'struct arr') " but there is no problem when I use either temp[i] or temp+i. Both var and temp are pointers. So why do I get this error ?

Another unrelated question, where or when do I have to free the dynamically allocated pointer temp. temp was dynamically allocated inside the function void inputArray(int); which is called in a loop in main.

Answer 1

(var+count) != var[count] but

*(var+count) == var[count]

and because

(*(var+count)).temp or (var+count)-> temp then

var[count].temp or (&var[count]) -> temp

MAKE SURE var is properly initialized and is referencing a valid object before using it!!