Problem with hash class

closed account (Lvk4GNh0)

Hi everyone, I'm trying to finish this program that will read in 15 names and then hash them using a hash class. My problem is that I can't figure out what is wrong with my insert function. During execution it will get to the use of the insert function and get a segmentation fault. If the use of the insert function is commented out, it will work just fine.

here's the driver

  #include<iostream>
#include <string>
using namespace std;
#include "hash.h"


int main (void)
{
 hash h;
 int p;
 string str,
        obj;
 bool success;
 char response;

 for(p=0;p<=14;p++)
  {
   cout<<"Enter a word \n";
   cin>>str;
   cout<<str<<endl;
   h.insert(str);

  }
 h.display();
 do
  {
   cout<<"Enter a word to be searched for \n";
   cin>>obj;
   success=h.search(obj);
   if(success)
    {
     cout<<"The word  was found \n";
    }
   else
    {
     cout<<"The word wasn't found \n";
    }
   cout<<"Search for more words (Y or N)? \n";
   cin>>response;
  }
  while (response == 'y' || response == 'Y');

 return 0;
}

here's the implementation file 

#include <iostream>
#include<string>
#include "hash.h"

using namespace std;

hash::hash()
{

 int i;
 cout<<"Entering constructor! \n";
  for(i=0;i<23;i++)
  {
   a[i]="?";
  }
}
void hash::insert(string word)
{
 int num,
     len,
     pos;
 cout<<"Entering insert";
 bool in;
 len=word.length()-1;
 num=int(word[0])+ int(word[len]);
 pos=num%23;
 if((a[pos]) != "?")
  {
   a[pos]=word;
  }
 else
  {
   pos=0;
   in=false;
   while(!in)
    {
     if((a[pos]) != "?")
      {
       a[pos]=word;
       in=true;
      }
     else
      {
       pos++;
      }
    }
    
   }
}
bool hash:: search (string  target)
{
 int j;
 bool found;
 j=0;
 found=false;
 while( (j<23) && (!found))
  {
   if(target == a[j])
    {
     found=true;
    }
   else
    {
     j++;
    }
  }
 return found;
}

void hash::display()
{
 int k;
 for(k=0;k<23;k++)
  {
   cout<<a[k]<<endl;
   cout<<"\n";
  }
}


and the header file 
#include <iostream>
#include <string>

using namespace std;

class hash
{
 public:

 hash();

 void insert(string word);

 bool search(string target);

 void display();

 private:
 string a[23];


 };

AbstractionAnon (6954)

One problem I see is in the while loop at lines 84-95. At line 93 you increment pos with no check as to whether you've reached the end of the array. Consider the iteration through the loop when pos = 22. Line 93 increments pos to 23 and returns to the top of the loop. Line 86 then proceeds to reference a[23] which is not a valid element of the array. Valid elements are 0-22.

closed account (Lvk4GNh0)

Well looking at it now, I realize that my logic is backwards. If the element in a[pos] is equal to a question mark, then the word should be stored there.The while loop should be enacted if the position isn't a question mark. I agree to that my while loop may need some revision.

I don't understand why the the program won't even reach the insert function though.

thanks,
Sean

AbstractionAnon (6954)

When I ran it, it reached the insert function, but crashed at line 88 trying to write into a[23], which is out of bounds.

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