/in/foo.cc: In function 'int main()':
/in/foo.cc:8:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int k=1;k<=n;k++)
              ~^~~
/in/foo.cc:9:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int i=0;i<=a;i++)
               ~^~~
/in/foo.cc:10:17: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
    for(int j=0;j<=b;j++)
                ~^~~
/in/foo.cc:14:15: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
  for(int i=0;i<=a;i++)
              ~^~~
/in/foo.cc:15:16: warning: comparison between signed and unsigned integer expressions [-Wsign-compare]
   for(int j=0;j<=b;j++)
               ~^~~