foo.cc: In function 'int main()':
foo.cc:4:13: warning: variable 'n' set but not used [-Wunused-but-set-variable]
     int k,i,n;
             ^
foo.cc:6:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&k);
     ~~~~~^~~~~~~~~

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