View Compilation Error

0_0_15784723_27462.cpp:4:3: error: expected primary-expression before 'double'
   double sum(int n);
   ^
0_0_15784723_27462.cpp:4:3: error: expected '}' before 'double'
0_0_15784723_27462.cpp:4:3: error: expected ',' or ';' before 'double'
0_0_15784723_27462.cpp:6:6: error: expected constructor, destructor, or type conversion before '(' token
 scanf("%d",&n);
      ^
0_0_15784723_27462.cpp:7:7: error: expected constructor, destructor, or type conversion before '(' token
 printf("%.0f",sum(n));
       ^
0_0_15784723_27462.cpp:8:1: error: expected unqualified-id before 'return'
 return 0;
 ^
0_0_15784723_27462.cpp:9:1: error: expected declaration before '}' token
 }
 ^