I am getting an error while compiling the c++ code, please help me out to fix this.

Waleed has the details, but you know you needn't cast this at all?

#include<iostream>
// #include<cstdlib>
/* You don't need that. */
using namespace std;

int main()
{
    int temp = 300;

    cout << "Address of variable temp:  " << &temp << std::endl;
    return 0;
}

That compiles fine, and will work, printing out the pointer address in Hex, as is normal.

As Waleed says, if you want it as an integer (and printed in traditional decimal), you need the integer type to be big enough. There's a std::intptr_t for this:

#include<iostream>
using namespace std;

int main()
{
    int temp = 300;

    cout << "Address of variable temp:  " << (std::intptr_t)&temp;
    return 0;
}

I am getting output in hexadecimal without using an unsigned keyword but , I just want to change output as an integer, can you tell me how to do this, and yes, my OS is a 64 bit.