“LNK1561 entry point must be defined” for simple program

Question

Here is my code:

#include <iostream>
#include <cmath>
using namespace std;

int main()
{
    int x;
    int y = pow(2, x);
    cin>>x;
    cout<< y;
    system("pause");
    return 0;
}

Why do I get a compile error? LNK1561 entry point must be defined

I am using Visual Studio Express.

Answer 1

You need to assign a value to x before it is used

int x;
int y = pow(2, x); // <--- what is the value of x here?

Try getting the value of x from the input first.

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    int x;
    cin >> x;
    int y = pow(2, x);
    cout<< y; 
    system("pause");
    return 0;
}

Answer 2

#include <iostream>
#include <cmath>
using namespace std;
int main()
{
    int x;
    //int y = pow(2, x);//(1)
    //cin>>x;//(2)

    //exchange the lines (2) and (1)
    cin>>x;//(2)
    int y = pow(2, x);//(1)
    cout<< y; 
    system("pause");
    return 0;
}