C++ Math exp2()

exp2(x) = 2x

float exp2(float x);
double exp2(double x);
long double exp2(long double x);
double exp2(integral x);

#include <iostream>
#include<math.h>
using namespace std;
int main()
{
 int x= 4;
 std::cout << "Value of x is : " <<x <<std::endl;
 cout<<"exp2(x) = "<<exp2(4);
 return 0;
}

Value of x is : 4
exp2(x) = 16

#include <iostream>
#include<math.h>
using namespace std;
int main()
{
 int x=-2;
 std::cout << "Value of x is : " <<x <<std::endl;
 cout<<"exp2(x) = "<<exp2(x);
 return 0;
}

Value of x is :-2
exp2(x) = 0.25