foo.cc: In function 'void init()':
foo.cc:17:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d%d",&m,&n);
     ~~~~~^~~~~~~~~~~~~~
foo.cc:20:18: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
             scanf("%d",&w[i][j]);
             ~~~~~^~~~~~~~~~~~~~~