foo.cc: In function 'int main()':
foo.cc:15:19: warning: left operand of comma operator has no effect [-Wunused-value]
   15 |  for(int i=1,j=1;i<=4,j<=4;i++,j++)
      |                  ~^~~
foo.cc:19:19: warning: left operand of comma operator has no effect [-Wunused-value]
   19 |  for(int i=1,j=4;i<=4,j>=1;i++,j--)
      |                  ~^~~

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