Multiple Definition of <'variable/function'>

I am trying to write a basic program with a candidate.h file, a candidate.cpp file, and a main.cpp file

I declared a function void readCandidates() in my candidate.h file.

I then define it in candidate.cpp as

void readCandidates ()
{
  cin >> nCandidates;
  string line;
  getline (cin, line);

  for (int i = 0; i < nCandidates; ++i)
    {
      getline (cin, candidateNames[i]);
      delegatesWon[i] = 0;
    }
}

The variables nCandidates, candidateNames[] and delegatesWon[] are all declared in candidate.h as well.

I also have

#ifndef CANDIDATE_H
#def CANDIDATE_H
...
#endif 

in my candidate.h file to ensure that it doesn't get defined twice.

When I run the command make main I get the error

/home/pmurray/cs250/Asst1/primaries.cpp:33: multiple definition of `candidate'
candidates.o:/home/pmurray/cs250/Asst1/candidates.cpp:8: first defined here
primaries.o: In function `assignDelegatesToCandidates()':
/home/pmurray/cs250/Asst1/primaries.cpp:37: multiple definition of `nCandidates'
candidates.o:/home/pmurray/cs250/Asst1/candidates.cpp:15: first defined here
primaries.o: In function `assignDelegatesToCandidates()':
/home/pmurray/cs250/Asst1/primaries.cpp:38: multiple definition of `delegatesWon'
candidates.o:/home/pmurray/cs250/Asst1/candidates.cpp:16: first defined here
candidates.o: In function `readCandidates()':

I tried putting extern before the declaration of one of the variables, and that resulted in the error

candidates.cpp:(.text+0x49): undefined reference to `candidateNames'
primaries.o: In function `findCandidate(std::basic_string<char, std::char_traits<char>, std::allocator<char> >)':
primaries.cpp:(.text+0x120): undefined reference to `candidateNames'
primaries.o: In function `printCandidateReport(int)':
primaries.cpp:(.text+0x1d8): undefined reference to `candidateNames' 

Anyone know what I am doing wrong?

candidates.cpp

#include <iostream>

using namespace std;
#include "candidates.h"

void readCandidates ()
{
  cin >> nCandidates;
  string line;
  getline (cin, line);

  for (int i = 0; i < nCandidates; ++i)
    {
      getline (cin, candidateNames[i]);
      delegatesWon[i] = 0;
    }
}

candidates.h

#ifndef CANDIDATES_H
#define CANDIDATES_H

#include <iostream>
#include <string>

using namespace std;

// Max # of candidates permitted by this program
extern const int maxCandidates = 10;

// Names of the candidates participating in this state's primary
extern string candidate[maxCandidates];

// Names of all candidates participating in the national election
extern std::string candidateNames[maxCandidates];

// How many candidates in the national election?
extern int nCandidates;

// How many delgates have been won by each candidate
extern int delegatesWon[maxCandidates];

extern int findCandidate (std::string name);


/**
 * read the list of candidate names, initializing their delegate counts to 0.
 */
void readCandidates ();

#endif // CANDIDATES_H

primaries.cpp (which is my main.cpp)

#include <iostream>
//#include "candidates.cpp"

using namespace std;

#include "candidates.h"

// How many delegates are assigned to the state being processed
int delegatesForThisState;

// How many candidates in the primary for the state being processed
int nCandidatesInPrimary;

// How many states participate in the election
int nStates;

// How many delegates in the election (over all states)
int totalDelegates = 0;

// How many votes were cast in the primary for this state
int totalVotes;

// How many votes wone by each candiate in this state's primary
int votesForCandidate[maxCandidates];


/**
 * For the most recently read primary, determine how many delegates have
 * been won by each candidate.
 */
int assignDelegatesToCandidates ()
{
  int remainingDelegates = delegatesForThisState;
  for (int i = 0; i < nCandidatesInPrimary; ++i)
    {
      int candidateNum = findCandidate(candidate[i]);
      int nDel = (delegatesForThisState * votesForCandidate[i] + (totalVotes-1)) / totalVotes;
      if (nDel > remainingDelegates)
    nDel = remainingDelegates;
      delegatesWon[candidateNum] += nDel;
      remainingDelegates -= nDel;
    }
}



/**
 * Find the candidate with the indicated name. Returns the array index
 * for the candidate if found, nCandidates if it cannot be found.
 */
int findCandidate (std::string name)
{
  int result = nCandidates;
  for (int i = 0; i < nCandidates && result == nCandidates; ++i)
    if (candidateNames[i] == name)
      result = i;
  return result;
}


/**
 * Print the report line for the indicated candidate
 */
int printCandidateReport (int candidateNum)
{
  int requiredToWin = (2 * totalDelegates + 2) / 3; // Note: the +2 rounds up
  if (delegatesWon[candidateNum] >= requiredToWin)
    cout << "开发者_如何学运维* ";
  else
    cout << "  ";
  cout << delegatesWon[candidateNum] << " " << candidateNames[candidateNum] << endl;
}



/**
 * read the info on one state's primaries
 */
void readState ()
{
  totalVotes = 0;
  cin >> nCandidatesInPrimary >> delegatesForThisState;
  totalDelegates += delegatesForThisState;  // "x += y" is a shorthand for "x = x + y"
  string word, line;
  getline (cin, line);
  for (int i = 0; i < nCandidatesInPrimary; ++i)
    {
      cin >> votesForCandidate[i];
      totalVotes = totalVotes + votesForCandidate[i];

      cin >> word;
      getline (cin, line);
      candidate[i] = word + line;
    }
}



/**
 * Generate the report on the national primary election.
 */
int main(int argc, char** argv)
{
  readCandidates();
  int nStates;
  cin >> nStates;
  for (int i = 0; i < nStates; ++i)
    {
      readState();
      assignDelegatesToCandidates();
    }
  for (int i = 0; i < nCandidates; ++i)
    {
      printCandidateReport(i);
    }
  return 0;
}

You declare variables and functions extern in header file, you still need to define them somewhere, the best in the .cpp file where you use them (candidates.cpp in your case).

Add to your candidates.cpp file the definitions of all those variables that you are using in your functions, that will fix your problem.

Btw, agreed that this is not a good programming form, but that is probably outside of the scope of this question. You should not need global variables because they don't need to be accessed outside of the implementation file (.cpp).