foo.cc: In function 'int main()':
foo.cc:6:13: warning: unused variable 'nn' [-Wunused-variable]
     int k,n,nn,x,xx,y,yy;
             ^~
foo.cc:6:18: warning: variable 'xx' set but not used [-Wunused-but-set-variable]
     int k,n,nn,x,xx,y,yy;
                  ^~
foo.cc:33:25: warning: 'k' may be used uninitialized in this function [-Wmaybe-uninitialized]
     cout<<n<<'='<<j<<'+'<<k;
     ~~~~~~~~~~~~~~~~~~~~^~~

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