data structures - C++ - run-time crashing of linear probing program -

i wrote program in c++ hashing using linear probing. code showing no error @ time of compilation when run it, computer shows notification program has stopped working. giving entire code below. please me out.

#include<iostream> #include<vector> using namespace std; class acc {     public:         int idata;         double ddata;         acc(int id,double dd)         {             idata = id;             ddata = dd;         }         void displayacc()         {             cout<<"idata = "<<idata<<"\n";             cout<<"ddata = "<<ddata<<"\n";         } }; class linear_hash {     private:         vector<acc*> hasharray;         int nelem;         acc* noelem;     public:         linear_hash(int max)         {             nelem = max;             hasharray.resize(nelem);             noelem = new acc(-1,1.1);             for(int = 0;i<max;i++)             {                 hasharray[i] = null;             }         }         int hashfunc(int key)         {             return key%nelem;         }         void insertacc(int id,double dd)         {             acc* newacc = new acc(id,dd);             int hashval = hashfunc(id);             while(hasharray[hashval]->idata!=-1&&hasharray[hashval]!=null)             {                 hashval++;                 hashval = hashval%nelem;             }             hasharray[hashval] = newacc;         }         acc* search(int key)         {             int hashval = key%nelem;             while(hasharray[hashval]->idata!=key&&hasharray[hashval]!=null)             {                 hashval++;                 hashval = hashval%nelem;             }             if(hasharray[hashval]->idata==key)             {                 return hasharray[hashval];             }             else                 return null;         }         bool deleteacc(int key)         {             int hashval = hashfunc(key);             while(hasharray[hashval]->idata!=key&&hasharray[hashval]!=null)             {                 hashval++;                 hashval = hashval%nelem;             }             if(hasharray[hashval]==null)                 return false;             else             {                 acc* ptemp = hasharray[hashval];                 hasharray[hashval] = noelem;                 delete ptemp;                 return true;             }         } }; int main(void) {     int key;     char val;     linear_hash lh(20);     lh.insertacc(100,100.1);     lh.insertacc(204,204.204);     lh.insertacc(105,105.10);     lh.insertacc(237,348.23);     lh.insertacc(209,923.23);     lh.insertacc(230,230.23);     lh.insertacc(403,348.34);     lh.insertacc(405,938.50);     lh.insertacc(450,348.23);     lh.insertacc(945,495.409);     while(val!='x')     {         cout<<"enter key searched\n";         cin>>key;         if(lh.search(key)==null)             cout<<key<<" not found\n";         else             lh.search(key)->displayacc();         cout<<"enter key deleted\n";         cin>>key;         if(lh.deleteacc(key))             cout<<key<<" has been deleted\n";         else             cout<<"invalid request\n";         cout<<"do want continue\n";         cin>>val;     }     return 0; } 

i unable use debugger in case don't know error is. have tried dry-running on paper wasn't able pin point bug.

near top of main this:

linear_hash lh(20); lh.insertacc(100,100.1); 

the first line sets vector:

for(int = 0;i<max;i++) {     hasharray[i] = null; } 

so, before second line have vector of nulls. second line this:

    acc* newacc = new acc(id,dd);     int hashval = hashfunc(id);     while(hasharray[hashval]->idata ... 

so, hasharray contains nulls, try @ hasharray[hashval]->idata i.e.

null->idata 

you should check hasharray[hashval]!=null before try it.