C: Pointers and Arrays Question

int i;
int a[20];

// Init all values to zero
memset(a, 0, sizeof(a));
for (i = 0; i < 20; i++) {
    printf("Value of %d is %dn", i, a[i]);
}

int i;
int a[20];
int * b;

memset(a, 0, sizeof(a));
b = a;
for (i = 0; i < 20; i++) {
    printf("Value of %d is %dn", i, *b);
    b++;
}

_main:
    pushl	%ebp
    movl	%esp, %ebp
    pushl	%edi
    pushl	%esi
    pushl	%ebx
    subl	$108, %esp
    call	___i686.get_pc_thunk.bx
"L00000000001$pb":
    leal	-104(%ebp), %eax
    movl	$80, 8(%esp)
    movl	$0, 4(%esp)
    movl	%eax, (%esp)
    call	L_memset$stub
    xorl	%esi, %esi
    leal	LC0-"L00000000001$pb"(%ebx), %edi
L2:
    movl	-104(%ebp,%esi,4), %eax
    movl	%eax, 8(%esp)
    movl	%esi, 4(%esp)
    movl	%edi, (%esp)
    call	L_printf$stub
    addl	$1, %esi
    cmpl	$20, %esi
    jne	L2
    addl	$108, %esp
    popl	%ebx
    popl	%esi
    popl	%edi
    popl	%ebp
    ret

_main:
    pushl	%ebp
    movl	%esp, %ebp
    pushl	%edi
    pushl	%esi
    pushl	%ebx
    subl	$124, %esp
    call	___i686.get_pc_thunk.bx
"L00000000001$pb":
    leal	-104(%ebp), %eax
    movl	%eax, -108(%ebp)
    movl	$80, 8(%esp)
    movl	$0, 4(%esp)
    movl	%eax, (%esp)
    call	L_memset$stub
    xorl	%esi, %esi
    leal	LC0-"L00000000001$pb"(%ebx), %edi
L2:
    movl	-108(%ebp), %edx
    movl	(%edx,%esi,4), %eax
    movl	%eax, 8(%esp)
    movl	%esi, 4(%esp)
    movl	%edi, (%esp)
    call	L_printf$stub
    addl	$1, %esi
    cmpl	$20, %esi
    jne	L2
    addl	$124, %esp
    popl	%ebx
    popl	%esi
    popl	%edi
    popl	%ebp
    ret

movl    -104(%ebp,%esi,4), %eax

movl    -108(%ebp), %edx
movl    (%edx,%esi,4), %eax

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

using namespace std;

typedef int64_t int64;
static int64 nsTime() {
  struct timespec tp;
  clock_gettime(CLOCK_REALTIME, &tp);
  return tp.tv_sec*(int64)1000000000 + tp.tv_nsec;
}

typedef int T;
size_t const N = 1024*1024*128;
T data[N];

int main(int, char**) {
  cout << "startingn";

  {
    int64 const a = nsTime();
    int sum = 0;
    for (size_t i=0; i<N; i++) {
      sum += data[i];
    }
    int64 const b = nsTime();
    cout << "Simple loop (indexed): " << (b-a)/1e9 << "n";
  }

  {
    int64 const a = nsTime();
    int sum = 0;
    T *d = data;
    for (size_t i=0; i<N; i++) {
      sum += *d++;
    }
    int64 const b = nsTime();
    cout << "Simple loop (pointer): " << (b-a)/1e9 << "n";
  }

  {
    int64 const a = nsTime();
    int sum = 0;
    for (size_t i=0; i<N; i++) {
      int a = sum+3;
      int b = 4-sum;
      int c = sum+5;
      sum += data[i] + a - b + c;
    }
    int64 const b = nsTime();
    cout << "Loop that uses more ALUs (indexed): " << (b-a)/1e9 << "n";
  }

  {
    int64 const a = nsTime();
    int sum = 0;
    T *d = data;
    for (size_t i=0; i<N; i++) {
      int a = sum+3;
      int b = 4-sum;
      int c = sum+5;
      sum += *d++ + a - b + c;
    }
    int64 const b = nsTime();
    cout << "Loop that uses more ALUs (pointer): " << (b-a)/1e9 << "n";
  }
}

char p1[ ] = "12345";
char* p2 = "12345";

char *ch = p1[ 3 ]; /* 4 */
ch = *(p2 + 3); /* 4 */

char p1[ ] = "12345";
char* p2 = "12345";

char *ch = p1[ 3 ]; /* 4 */
ch = *(p2 + 3); /* 4 */