---

Lỗi biên dịch:

Main.cc:4:11: error: ‘::main’ must return ‘int’
 void main() {
           ^
Main.cc: In function ‘int main()’:
Main.cc:7:17: error: ‘atan’ was not declared in this scope
     double pi = atan(1.0) * 4; 
                 ^~~~
Main.cc:7:17: note: suggested alternative: ‘atol’
     double pi = atan(1.0) * 4; 
                 ^~~~
                 atol
Main.cc:7:12: warning: unused variable ‘pi’ [-Wunused-variable]
     double pi = atan(1.0) * 4; 
            ^~