foo.cc: In function 'int main()':
foo.cc:17:13: warning: unused variable 'c' [-Wunused-variable]
     int a,b,c,d;
             ^
foo.cc:17:15: warning: unused variable 'd' [-Wunused-variable]
     int a,b,c,d;
               ^
foo.cc:12:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d",&n,&m);
     ~~~~~^~~~~~~~~~~~~~
foo.cc:14:14: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d%d",&vn[i].id,&vn[i].num);
         ~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~
foo.cc:26:16: warning: 'b' may be used uninitialized in this function [-Wmaybe-uninitialized]
     ansi=vn[b].id;
          ~~~~~~^~

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