error: expected a ';', bug in Intellisense when building? - c++

Question

I got an error in Visual Studio 2019, when building and using IntelliSense at the same time, which said that it expected a ';' (CODE: E0065 and the error is supposed to be on line 9), I am extremely confused because this is my first time getting an error like this when defining functions because it is also my first time defining functions in c++, I really don't know where I could be missing a semi colon. The program doesn't run.
#include <iostream>
using namespace std;
int main() {
const double pi{3.14159};
double calc_area_circle(double radius) {
return pi * (radius * radius);
}
void area_circle() {
double radius{};
cout << "Enter the radius of the circle: ";
cin >> radius;
cout << "The area of the circle with radius " << radius << " is " << calc_area_circle(radius) << endl;
}
return 0;
}
If any one could clear this up for me, I would really appreciate it.

Answer 1

Nesting of function definition (defining functions inside another functions) is not allowed in C++ unless you use lambda functions.
Put the function definitions outside the function
#include <iostream>
using namespace std;
const double pi{3.14159};
double calc_area_circle(double radius) {
return pi * (radius * radius);
}
void area_circle() {
double radius{};
cout << "Enter the radius of the circle: ";
cin >> radius;
cout << "The area of the circle with radius " << radius << " is " << calc_area_circle(radius) << endl;
}
int main() {
return 0;
}
or convert them to lambda function
#include <iostream>
using namespace std;
int main() {
const double pi{3.14159};
const auto calc_area_circle = [&](double radius) -> double {
return pi * (radius * radius);
};
const auto area_circle = [&]() {
double radius{};
cout << "Enter the radius of the circle: ";
cin >> radius;
cout << "The area of the circle with radius " << radius << " is " << calc_area_circle(radius) << endl;
};
return 0;
}
Note: these programs will do nothing because the defined functions are not called.