View Compilation Error

0_0_15231891_30436.cpp:18:10: error: 'N' was not declared in this scope
 double a[N];  
          ^
0_0_15231891_30436.cpp: In function 'int main()':
0_0_15231891_30436.cpp:27:26: error: 'a' was not declared in this scope
             scanf("%lf",&a[i]);  
                          ^
0_0_15231891_30436.cpp:32:13: error: 'a' was not declared in this scope
             a[x]+=w;  
             ^
0_0_15231891_30436.cpp:35:14: error: 'a' was not declared in this scope
         sort(a+1,a+1+n);  
              ^