"Undefined symbols" error while compiling project

I'm trying to compile a project in C ++, but it's giving the following error:

Undefined symbols for architecture x86_64:

  "knapSack(int, int*, int*, int)", referenced from:

      _main in main-b722ae.o

ld: symbol(s) not found for architecture x86_64

clang: error: linker command failed with exit code 1 (use -v to see invocation)

Any idea what this might be?

I'm using the MacOs X 10.9 system. Here is the snippet of the code where the error is being pointed out:

// Returns the maximum value that can be put in a knapsack of capacity W

int knapSack(int W, int wt[], int val[], int n)
{
   int i, w, profit, cont = 0;

   item* K = NULL;

   //Build table K[][] in bottom up manner

   for (i = 0; i <= n; i++)    
   {    
       for (w = 0; w <= W; w++)   
       {    
           if (i==0 || w==0) 
           {
               profit = 0;

               K = insertItem(profit, K);
           }

           else if (wt[i-1] <= w)
           { 
               profit = max(val[i-1] + returnItem(K, (i-1), (w-wt[i-1]), W),  returnItem(K, (i-1), w, W));

               K = insertItem(profit, K);
           }

           else  
           {
               profit = returnItem(K, (i-1), w, W);

               K = returnItem(profit, K); 
           }

           cont++;

            if(cont % 1000 == 0)
            {

                cout << "i = "<< i << "w = " << w << "profit = " << profit << endl;//printf("i = %d, w = %d, profit = %d \n", i, w, profit);

            }
       }
   } 
   return returnItem(K, (i-1), (w-1), W);
}