foo.cc: In function 'int main()':
foo.cc:10:21: warning: iteration 18 invokes undefined behavior [-Waggressive-loop-optimizations]
   10 |                 a[i]=a[i-1]+a[i-2];
      |                 ~~~~^~~~~~~~~~~~~~
foo.cc:8:22: note: within this loop
    8 |         for(int i=2;i<=20;i++)
      |                     ~^~~~
foo.cc:14:32: warning: iteration 19 invokes undefined behavior [-Waggressive-loop-optimizations]
   14 |                 sum+=(float)a[i]/(float)a[i-1];
      |                             ~~~^
foo.cc:12:22: note: within this loop
   12 |         for(int i=1;i<=20;i++)
      |                     ~^~~~

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