foo.cc: In function 'int cal(int)':
foo.cc:4:9: warning: unused variable 'sum' [-Wunused-variable]
    4 |     int sum=0;
      |         ^~~
foo.cc:14:1: warning: no return statement in function returning non-void [-Wreturn-type]
   14 | }
      | ^
foo.cc: In function 'int main()':
foo.cc:19:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
   19 |     scanf("%d",&n);
      |     ~~~~~^~~~~~~~~

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