foo.cc: In function 'int main()':
foo.cc:6:29: error: 'a' was not declared in this scope
  for(int i=1;i<=n;i++) cin>>a[i];
                             ^
foo.cc:12:25: error: 'ans' was not declared in this scope
   for(int i=a;i<=b;i++) ans+=a[i];
                         ^~~
foo.cc:12:25: note: suggested alternative: 'abs'
   for(int i=a;i<=b;i++) ans+=a[i];
                         ^~~
                         abs
foo.cc:12:33: error: invalid types 'int[int]' for array subscript
   for(int i=a;i<=b;i++) ans+=a[i];
                                 ^
foo.cc:13:9: error: 'ans' was not declared in this scope
   cout<<ans<<endl;
         ^~~
foo.cc:13:9: note: suggested alternative: 'abs'
   cout<<ans<<endl;
         ^~~
         abs

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