View Compilation Error

0_0_38681724_17519.cpp: In function 'int main()':
0_0_38681724_17519.cpp:15:39: error: 'b' was not declared in this scope
   15 |                 for (int i=n-1;i;i--) b[i]+=1.0/i;
      |                                       ^
0_0_38681724_17519.cpp:17:49: error: 'b' was not declared in this scope
   17 |                         long double val=1.0*k/n*b[k];
      |                                                 ^