Thread: Hash table help

Hi, im getting these errors for my code, can someone help please.

hash.cpp: In function 'int main()':
hash.cpp:50: error: invalid conversion from 'int' to 'data*'
hash.cpp:51: error: invalid conversion from 'data*' to 'int'
hash.cpp:51: error: initializing argument 1 of 'data::data(int)'
linhash.h: In member function 'int linHashtable<dataType>::insert(const dataType&) [with dataType = data]':
hash.cpp:51: instantiated from here
linhash.h:60: error: passing 'const data' as 'this' argument of 'int data::getHashval(int)' discards qualifiers

Code:

#include <iostream>
#include "linhash.h"

/* Small program to explore using hash tables.

   1. The hash table takes up to 400 items
   2. The program generates 400 random six digit numbers.
   3. It uses a hashing routine to place them in the hash table.
   4. The program prints a report on the percantage of clashes that 
      occur for every 20 numbers placed in the table.
*/ 

using namespace std;

struct data
{
   int x;
   
   data() : x(-1) {
   }
   
   data(int n) : x(n) {
   }
   
   bool empty() {
      return (x < 0);
   }
   
   int getHashval(int range) {
      return (x % range);
   }
};

int main()
{
   const int SIZE = 400;
   int count, totalClashes=0;
   int clashes = 0, numClashes;
   data *dataPtr;
   
   // declare linera hash table
   linHashtable<data> hashTable(SIZE);

   // initialise the random number generator
   srand(1);

   // generate 400 six digit numbers and put in hash table
   for (count=1; count<=SIZE; count++) {
      // create 6 digit number and then insert in hash table
      dataPtr = new data(rand() % 1000000);    
      numClashes = hashTable.insert(dataPtr);
      
      // build up hashing data
      if (numClashes > 0) {
         totalClashes += numClashes;
         clashes++;
      }
         
      // print a report with each set of 20 numbers added to table
      if ((count+1) % 20 == 0)
      {
         cout << "% full = " << (count+1) * 100 / SIZE << "\n";
         cout << "% clashing = " << clashes * 100 / (count+1) << "\n";
         cout << "ave search time = " << (count+1 + totalClashes) / (count+1) << "\n\n";
      }
   }

   return 0;
}

1. You can either do new or you can use an initializer, none of this "both at the same time" sort of thing. According to the error message, hashTable.insert takes a data, not a data*, so there is no reason or excuse for having a pointer to data in the first place.

2. Since hashTable.insert treats its data as const, all the class methods required by insert must be const as well; specifically, getHashVal must be a const function.