/in/foo.cc: In function 'int sum(int*, int)':
/in/foo.cc:16:20: warning: left operand of comma operator has no effect [-Wunused-value]
  for(int i = 1 ; i <= n, i++ ){
                  ~~^~~~
/in/foo.cc:16:30: error: expected ';' before ')' token
  for(int i = 1 ; i <= n, i++ ){
                              ^
/in/foo.cc: In function 'int main()':
/in/foo.cc:25:8: error: unable to find numeric literal operator 'operator""n'
  int a[2n+1];
        ^~
/in/foo.cc:25:8: note: use -std=gnu++11 or -fext-numeric-literals to enable more built-in suffixes
/in/foo.cc:27:16: error: 'a' was not declared in this scope
   scanf("%d", &a[i]);
                ^
/in/foo.cc:35:46: error: 'a' was not declared in this scope
     if(f[i][j]< (f[i][k] + f[k + 1][j] + sum(a,j) - sum(a,i-1))){
                                              ^