How come this const. expression does not compile? - variables

Question

#include <iostream>
using namespace std;
int main()
{
constexpr double GetPi() {return 22.0/7;}
cout << GetPi() << endl;
}
No idea what is going on here. Please help me.
I've tried to compile this and even tried to re-format the code but it doesn't really help much. I thought this was the correct way you did things? What's going on here? It's a constant expression.
Here is the compilation error:
C:\Windows\system32\cmd.exe /C "C:/TDM-GCC-64/bin/mingw32-make.exe -j4` SHELL=cmd.exe -e -f Makefile"
"----------Building project:[ Constant_Expression - Debug ]----------"
mingw32-make.exe[1]: Entering directory 'C:/Program Files/CodeLite/CPP/Constants/Constant_Expression'
codelite-cc C:/TDM-GCC-64/bin/g++.exe -c "C:/Program Files/CodeLite/CPP/Constants/Constant_Expression/main.cpp" -g -O0 -std=c++11 -Wall -o ./Debug/main.cpp.o -I. -I.
C:/Program Files/CodeLite/CPP/Constants/Constant_Expression/main.cpp: In function 'int main()':
C:/Program Files/CodeLite/CPP/Constants/Constant_Expression/main.cpp:7:30: error: a function-definition is not allowed here before '{' token
constexpr double GetPi() {return 22.0/7;}
^
C:/Program Files/CodeLite/CPP/Constants/Constant_Expression/main.cpp:8:19: error: 'GetPi' was not declared in this scope
cout << GetPi() << endl;
^
mingw32-make.exe[1]: *** [Debug/main.cpp.o] Error 1
Constant_Expression.mk:93: recipe for target 'Debug/main.cpp.o' failed
mingw32-make.exe[1]: Leaving directory 'C:/Program Files/CodeLite/CPP/Constants/Constant_Expression'
mingw32-make.exe: *** [All] Error 2
Makefile:4: recipe for target 'All' failed
3 errors, 0 warnings

Answer 1

In C++ you are not allowed to define a function inside another function. (unlike closures in javascript).
You have to define GetPI() outside the main() function
#include <iostream>
using namespace std;
constexpr double GetPi() {return 22.0/7;}
int main()
{
cout << GetPi() << endl;
}