invalid operands of types ‘int’ and ‘const char [15]’ to binary ‘operator<<’ ^

Question

I'm trying to do a simple math problem, but I keep getting this error message. What is wrong? I'm using cloud9 ide.

/home/ubuntu/workspace/Sphere.cpp: In function 'int main()': /home/ubuntu/workspace/Sphere.cpp:20:63: error: invalid operands of types 'int' and 'const char [15]' to binary 'operator<<' cout << "The area of the circle is: " << 3.14*meters^2 << "meters squared" << endl;

Here is the entire code:

#include <iostream>

using namespace std;

int main() {

    // Declare the radius
    int meters;
    cout << "Please enter the radius in meters: ";
    cin >> meters;

    // Calculate Diameter

    cout << "The diameter of the circle is: " << meters*2 << "m" << endl;

    //Calculate Area
    double PI;
    PI = 3.14;

    cout << "The area of the circle is: " << 3.14*meters^2 << "meters squared" << endl;

}

Answer 1

In C++, the ^ operator does not mean exponentiation. It means to do a bitwise-XOR operation on two integer values.

And since ^ has lower precedence than << , the compiler interprets your statement as

((cout << "The area of the circle is: ") << (3.14*meters)) ^
    ((2 << "meters squared") << endl);

and gets hung up on what 2 << "meters squared" is supposed to do.

In general, C++ has std::pow for exponentiation. But it's overkill for just squaring a number, and it's probably better to just multiply that number by itself:

std::cout << "The area of the circles is: " << 3.14*meters*meters 
          << " meters squared" << std::endl;