foo.c: In function 'main':
foo.c:15:18: warning: iteration 20 invokes undefined behavior [-Waggressive-loop-optimizations]
   15 |         sum=sum+a[i+1]/a[i];
      |                 ~^~~~~
foo.c:14:22: note: within this loop
   14 |         for(int i=0;i<=20;i++)
      |                     ~^~~~

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