Main.cc: In function ‘int main()’:
Main.cc:12:25: error: unable to find numeric literal operator ‘operator""i’
q=4*(pow(-1,i)/(2i+1));
^~
Main.cc:12:25: note: use -std=gnu++11 or -fext-numeric-literals to enable more built-in suffixes
Main.cc:10:10: warning: ignoring return value of ‘int scanf(const char*, ...)’, declared with attribute warn_unused_result [-Wunused-result]
scanf("%d",&n);
~~~~~^~~~~~~~~