foo.c: In function 'main':
foo.c:28:5: warning: ignoring return value of 'scanf', declared with attribute warn_unused_result [-Wunused-result]
   28 |     scanf("%d", &n);
      |     ^~~~~~~~~~~~~~~
foo.c: In function 'prime':
foo.c:7:5: warning: 'k' may be used uninitialized in this function [-Wmaybe-uninitialized]
    7 |     for ( i = 2; i <= k; i++) {
      |     ^~~

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