simple sorting using thrust not working

I have a cuda thrust program as

#include <stdio.h>
#include<iostream>
#include <cuda.h>
#include <thrust/sort.h>



// main routine that executes on the host
int main(void)
{
  int *a_h, *a_d;  // Pointer to host & device arrays
  const int N = 10;  // Number of elements in arrays
  size_t size = N * sizeof(int);
  a_h = (int *)malloc(size);        // Allocate array on host
  cudaMalloc((void **) &a_d, size);// Allocate array on device
  std::cout<<"enter the 10 numbers";
  // Initialize host array and copy it to CUDA device
  for (int i=0; i<N; i++) 
  {
      std::cin>>a_h[i];
  }
  for (int i=0; i<N; i++) printf("%d %d\n", i, a_h[i]);
  cudaMemcpy(a_d, a_h, size, cudaMemcpyHostToDevice);
  thrust::sort(a_d, a_d + N);
  // Do calculation on device:

  cudaMemcpy(a_h, a_d, sizeof(int)*N, cudaMemcpyDeviceToHost);
  // Print results
  for (int i=0; i<N; i++) printf("%d %d\n", i, a_h[i]);
  // Cleanup
  free(a_h); cudaFree(a_d);
}

but it is not running to give the desired output.

Are we supposed to use the host vector and device vector for sorting in thrust????

For device operations you should use either a device pointer, or a device_vector iterator, not raw pointers. Raw pointers (that point to host memory) can be used for operations on the host.

So if you modify your code as follows:

#include <thrust/device_ptr.h>
...
thrust::device_ptr<int> t_a(a_d);  // add this line before the sort line
thrust::sort(t_a, t_a + N);        // modify your sort line

I believe it will work for you.

You may wish to read the thrust quick start guide. In particular note this section:

You may wonder what happens when a "raw" pointer is used as an argument to a Thrust function. Like the STL, Thrust permits this usage and it will dispatch the host path of the algorithm. If the pointer in question is in fact a pointer to device memory then you'll need to wrap it with thrust::device_ptr before calling the function