View Compilation Error

0_0_26459166_13651.cpp: In function 'int main()':
0_0_26459166_13651.cpp:13:1: error: expected ';' before 'double'
 double f(int n, double a[], double x){ 
 ^
0_0_26459166_13651.cpp:13:38: error: a function-definition is not allowed here before '{' token
 double f(int n, double a[], double x){ 
                                      ^
0_0_26459166_13651.cpp:21:12: error: expected '}' at end of input
 return sum;}
            ^