View Compilation Error

0_0_25575280_20666.cpp: In function 'int main()':
0_0_25575280_20666.cpp:7:40: error: 'a' was not declared in this scope
   for(int i = 0;i < n; i++)scanf("%d",&a[i]),aa^=a[i];
                                        ^
0_0_25575280_20666.cpp:8:40: error: 'y' was not declared in this scope
   for(int i=1;i<n;i++)scanf("%d%d",&x,&y);
                                        ^
0_0_25575280_20666.cpp:9:8: error: 'sum' was not declared in this scope
   puts(sum?"Q":"D");
        ^