foo.cc: In function 'int main()':
foo.cc:8:12: warning: unused variable 'N' [-Wunused-variable]
  int const N=4;
            ^
foo.cc:9:14: warning: unused variable 'n' [-Wunused-variable]
  int a[4][4],n,c,i,j,k,sum=0;
              ^
foo.cc:9:16: warning: unused variable 'c' [-Wunused-variable]
  int a[4][4],n,c,i,j,k,sum=0;
                ^
foo.cc:9:22: warning: unused variable 'k' [-Wunused-variable]
  int a[4][4],n,c,i,j,k,sum=0;
                      ^

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