c++ question:After assigning value to a variable,the other variable changed - c++

Question

Following codes are my own API for index prior queue.When I test insert function,I get wrong answer.Then I debug codes,I found that the value of array qp changed after executing sentence----item[k]=vwhich is in insert function.Why the value of array qp changed after assigning value to array item?
template <class T>
class IndexPriorQueue{
private:
int index;//the num of items
int size;//capacity
int* pq;//index binaryheap
int* qp;//qp[pq[i]]=pq[qp[i]]=i
T* item;//item array;
public:
IndexPriorQueue(int qsize){//constructor function
size=qsize;
index=0;
pq=new int(size+1);
qp=new int(size+1);
item=new T(size+1);
for(int i=0;i<size+1;i++)
qp[i]=-1;
}
void insert(int k,T v){
if(contain(k)){
cout<<"index is already in queue"<<endl;
return;
}
//cout<<"insert"<<endl;
item[k]=v;//debug,after excuting this sentence,the value of qp exchanged??
pq[++index]=k;
qp[k]=index;
swim(index);
}
bool contain(int k){
return qp[k]!=-1?1:0;
}
void swim(int j){
while(j>1){
if(item[pq[j/2]]<item[pq[j]]){
exch(j/2,j);
j=j/2;
}else{
break;
}
}
}
void exch(int m,int n){
int temp=pq[m];
pq[m]=pq[n];
pq[n]=temp;
qp[pq[m]]=m;
qp[pq[n]]=n;
}
void display(){
cout<<"item:";
for(int i=1;i<size+1;i++){
cout<<item[i]<<" ";
}
cout<<endl;
cout<<"pq:";
for(int i=1;i<size+1;i++){
cout<<pq[i]<<" ";
}
cout<<endl;
cout<<"qp:";
for(int i=1;i<size+1;i++){
cout<<qp[i]<<" ";
}
cout<<endl;
}
};
Following codes are main function
int main(){
cout<<"before insert:"<<endl;
IndexPriorQueue<char> ipq(10);
ipq.display();
ipq.insert(1,'a');
cout<<"after insert:"<<endl;
ipq.display();
return 0;
}

Answer 1

The problems is your allocations. Take for example
new T(size+1)
That allocates one object of type T and initializes it to the value size + 1 (i.e. it calls the T constructor with size + 1).
If you need to allocate an "array" you should use square brackets [] as in
new T[size+1]
That will allocate an array of size + 1 number of T objects.
A much better solution though, is to use std::vector instead of doing it all manually yourself.