_global_ void add(int *a, int *b, int *c)

{

    int index = threadIdx.x + blockIdx.x * blockDim.x;

    c[index] = a[index] + b[index];

}

#define N (2048*2048)

#define THREAD_PER_BLOCK 512

int main()

{

    int *a, *b, *c;            //host copies of a, b, c

    int *d_a, *d_b, *d_c;    //device copies of a, b, c

    int size = N * sizeof(int);

    //Alloc space for device copies of a, b, c

    cudaMalloc((void **)&d_a, size);

    cudaMalloc((void **)&d_b, size);

    cudaMalloc((void **)&d_c, size);

    //Alloc space for host copies of a, b, c and setup input values

    a = (int *)malloc(size); random_ints(a, N);

    b = (int *)malloc(size); random_ints(b, N);

    c = (int *)malloc(size);

    //Copy the data into device

    cudeMemcpy(d_a, a, size, cudaMemcpyHostToDevice);

    cudaMemcpy(d_b, b, size, cudaMemcpyHostToDevice);

    //Launch add() kernel on GPU with N blocks

    add<<<N/THREADS_PER_BLOCK,THREADS_PER_BLOCK>>>(d_a, d_b, d_c);

    //Copy result back to host

    cudaMemcpy(c, d_c, size, cudaMemcpyDeviceToHost);

    //Cleanup

    free(a); free(b); free(c);

    cudeFree(d_a); cudaFree(d_b); cudaFree(d_c);

    return ;

}

/**** What's the function of random_ints****/

void random_ints(int* a, int N)

{

 int i;

 for (i = ; i < N; ++i)

 a[i] = rand();

}