lst-0014-godb.cpp
//#(compile) c++; compiler:g132; options:-O3 -std=c++23; libs:-
// https://godbolt.org/z/oh91YvaqT
#include <iostream>
void twice(double &num) { // output parameter as modifiable reference
num *= 2.0;
}
int main() {
double num = 7.25;
twice(num);
std::cout << num << "\n"; // now 14.5
}