Pointer to an array and Array of pointers

Question

As I am just a learner, I am confused about the above question. How is a pointer to an array different from array of pointers? Please explain it to me, as I will have to exp

Answer 1

I often resort to pen and paper when thinking about c pointers.

Pointer to an array

[a] -> [b]
       [c]
       [d]
        .
        .
        .

An array of pointers

[a] -> [j]
[b] -> [k]
[c] -> [l]
 .      .
 .      .
 .      .

A pointer to an array contains the memory location of an array. Whereas an array of pointers contains lots of memory locations, which contain single values (or possibly other arrays, or arrays of pointers ;).

Pointer to an array

#include 
#include 

void main(void) {
    int i;
    int *ptr, *loopPtr;
    ptr = malloc(10 * sizeof(int)); // allocate an array of 10 ints on the heap

    loopPtr = ptr;            // copy pointer into temp pointer 
    for(i=0; i < 10; i++) {
        *loopPtr = i;         // dereference pointer and store i in it
        loopPtr++;            // move pointer to next memory location
    }

    loopPtr = ptr;            // copy pointer into temp pointer
    for(i=0; i < 10; i++) 
        printf("%d, ",*(loopPtr++)); // move across array printing
    printf("\n");
    free(ptr);               // free memory allocated on the heap
}

An array of pointers

#include 
#include 

void main(void) {
    int i;
    int *ptr[10];            // an array of pointers

    // allocate 10 ints on the heap pointed to by an array
    for(i=0; i < 10; i++)
        ptr[i] = malloc(sizeof(int));

    for(i=0; i < 10; i++)
        *ptr[i] = i;         // dereference pointer and store i in it

    for(i=0; i < 10; i++)    // iterate through array and dereference pointers
        printf("%d, ",*ptr[i]);
    printf("\n");

    for(i=0; i < 10; i++)
        free(ptr[i]);
}

The best way to contrast the difference is probably with the malloc() calls, one returns a pointer to an array of 10 ints and the other returns 10 pointers to individual ints.