Please tell the LNK2019 error solution

I am getting an error that is

Socket.obj : error LNK2019: unresolved external symbol "int __cdecl calc_check(int)" (?calc_check@@YAHH@Z) referenced in function _main

This is mine socket.cpp

int main()
{
int hh=2;

    //int chkvalue=calculatechecksum();
    int chkvalue=calc_check(hh);
}

This is mine checksum.c

//===================================================== file = checksum.c =====

//----- Include files ---------------------------------------------------------
#include <stdio.h>                  // Needed for printf()
#include <stdlib.h>                 // Needed for rand()
#include <windows.h>
#include<conio.h>
#include <stdint.h>
#include"Constant.h"

//----- Type defines ----------------------------------------------------------
typedef unsigned char      byte;    // Byte is a char
typedef unsigned short int word16;  // 16-bit word is a short int
typedef unsigned int       word32;  // 32-bit word is an int

//----- Defines ---------------------------------------------------------------
#define BUFFER_LEN        6      // Length of buffer
//extern char data[6];
//char data[6]="CM00";
 extern char data[6]="CM00";
   word16      check;  
//----- Prototypes ------------------------------------------------------------
word16 checksum(char *addr, word32 count);
//int calc_check(int);
//===== Main program ==========================================================
int calc_check(int w)
{
 //byte        buff[BUFFER_LEN]; // Buffer of packet bytes

          // 16-bit checksum value
  word32      i;                // Loop counter

  // Load buffer with BUFFER_LEN random bytes
  for (i=0; i<BUFFER_LEN; i++)
  {
    //buff[i] = (byte) rand();
	data[i]=(byte) rand();
  }

  // Compute the 16-bit checksum
  //check = checksum(buff, BUFFER_LEN);
  check = checksum(data, BUFFER_LEN);

  // Output the checksum
  printf("checksum = %04X \n", check);
  return check;
  
}

//=============================================================================
//=  Compute Internet Checksum for count bytes beginning at location addr     =
//=============================================================================
word16 checksum(char *addr, word32 count)
{
  register word32 sum = 0;

  // Main summing loop
  while(count > 1)
  {
    //sum = sum + *((word16 *) addr)++;
	  sum += *((word16 *) addr)++;
    count = count - 2;
  }

  // Add left-over byte, if any
  if (count > 0)
    sum = sum + *((byte *) addr);

  // Fold 32-bit sum to 16 bits
  while (sum>>16)
    sum = (sum & 0xFFFF) + (sum >> 16);

  return(~sum);
}

This is mine header file(constant.h) which is included in socket.cpp

int calc_check(int);

Tags: C++, C, VC++, Visual Studio