foo.c: In function 'main':
foo.c:21:9: warning: statement with no effect [-Wunused-value]
   21 |         for (a; a < m; a++)
      |         ^~~
foo.c:26:9: warning: statement with no effect [-Wunused-value]
   26 |         for (b; b < n; b++)
      |         ^~~

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