View Compilation Error

0_0_27275150_30023.cpp: In function 'int main()':
0_0_27275150_30023.cpp:8:1: error: expected primary-expression before 'if'
 if(n==0){
 ^
0_0_27275150_30023.cpp:10:17: error: expected ';' before ')' token
 for(i=0;i<=n,i++)
                 ^
0_0_27275150_30023.cpp:11:7: error: 'a' was not declared in this scope
 {sum+=a;
       ^