Question

what is the difference between the following block of code :

#include<iostream>
using namespace std;
int main()
{
    int *p;
    float *q;
    cout<<p<<"\n"<<q;
}

and this code :

#include<iostream>
using namespace std;
int main()
{
    int *p;
    float *q;
    p = new int;
    q = new float;
    cout<<p<<"\n"<<q;
}

In both the cases the pointers are allocated some memory right?

Then why should i use the new operator?

Answer 1

No, int *p and float *p declare pointers, but they are not initialised, so they each point to a random address in memory. In particular, they do not point to memory space allocated to your program.

The second piece of code correctly allocates memory and stores the address of that memory in the two pointers. However, note that your code never de-allocates the memory, so you have a memory leak. You’d have to use delete p and delete q at the end of the program to avoid this.