No viable overloaded '=' c++

Question

I'm getting the error message "no viable overloaded '='". This is the code as I have it now

#include <iostream>
#include <cmath>
using namespace std;
int main() {
    auto n=0;
    int p=0;
    cout << "enter number n:"<< endl;
    cin >> n ;
    cout << p=pow(2,n)*n! << endl; //this is where I get the error message
    cout << "the product is:" << endl;
    cout << p << endl;
    return 0;
}

Can anyone tell me what I have wrong?

Answer 1

According to C++ Operator Precedence, operator << has precedence over operator =.

This means

cout << p=pow(2,n)*n! << endl;

is read as

(cout << p)=(pow(2,n)*n! << endl);

which has no sense. Protect you assignment with parenthesis:

cout << (p=pow(2,n)*n!) << endl;

or better yet, split it in two statements:

p=pow(2,n)*factorial(n); // n! does not exist in C++.
cout << p << endl;