int arr[] = {1,2,3,4};
char arr[] = {'a','b','c',0};

#include "stdio.h"

int main()
{
  /*
  author: www.nowamagic.net
  */
  int i, length;
  int arr[] = {1,2,3,4};

  length = sizeof(arr) / sizeof(int);
  printf("sizeof(arr)为：%d\n", sizeof(arr));
  printf("sizeof(int)为：%d\n", sizeof(int));
  printf("数组长度为：%d\n", length);
  for(i = 0; i < length; i++)
  {
    printf("%d\n", arr[i]);
  }

  return 0;
}

sizeof(arr)为：16
sizeof(int)为：4
数组长度为：4
1
2
3
4

#include "stdio.h"

int main()
{
  /*
  author: www.nowamagic.net
  */
  int i, length;
  char arr[] = {'a','b','c',0};

  length = sizeof(arr) / sizeof(char);
  printf("sizeof(arr)为：%d\n", sizeof(arr));
  printf("sizeof(char)为：%d\n", sizeof(char));
  printf("数组长度为：%d\n", length);
  for(i = 0; i < length; i++)
  {
    printf("%c\n", arr[i]);
  }

  return 0;
}

sizeof(arr)为：4
sizeof(char)为：1
数组长度为：4
a
b
c

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

#define     K    15
#define     DIM   10
#define     LOOP  1000000

int main(int argc, char** argv)
{
    double     o_centers[K*DIM];
    int       i = 0, j = 0, k = 0;


    MPI_Init(&argc, &argv);

    printf("Start to test array assign...\n");
    double     starttime1 = MPI_Wtime();
    for(k = 0; k < LOOP; k++)
        for(i = 0; i < K; i++)
            for(j = 0; j < DIM; j++)
                o_centers[j + i*DIM] = 0;
    double     endtime1 = MPI_Wtime();
    printf("Array assign takes %5.12f seconds...\n", endtime1 - starttime1);


    printf("Start to test memset assign...\n");
    double     starttime2 = MPI_Wtime();
    for(k = 0; k < LOOP; k++)
        memset(o_centers, 0, K*DIM*sizeof(double));
    double     endtime2 = MPI_Wtime();
    printf("Memset assign takes %5.12f seconds...\n", endtime2 - starttime2);

    MPI_Finalize();
    return 0;
}

Start to test array assign...
Array assign takes 0.624787092209 seconds...
Start to test memset assign...
Memset assign takes 0.052299976349 seconds...

int arr[8]={1,2,3,4};

int arr[8]={1,2,3,4,0,0,0,0};