View Compilation Error

0_0_25930024_21442.cpp: In function 'int main()':
0_0_25930024_21442.cpp:30:19: error: 'a' was not declared in this scope
    scanf("%I64d",&a[i]);
                   ^
0_0_25930024_21442.cpp:34:5: error: 'a' was not declared in this scope
   r=a[0];
     ^