foo.cc:35:11: error: redefinition of 'const int maxn'
 const int maxn=+5;
           ^~~~
foo.cc:3:11: note: 'const int maxn' previously defined here
 const int maxn=+5;
           ^~~~
foo.cc:36:5: error: redefinition of 'int n'
 int n;
     ^
foo.cc:5:9: note: 'int n' previously declared here
 int i,j,n;
         ^
foo.cc: In function 'int main()':
foo.cc:37:5: error: redefinition of 'int main()'
 int main() {
     ^~~~
foo.cc:21:5: note: 'int main()' previously defined here
 int main() {
     ^~~~
foo.cc: In function 'int main()':
foo.cc:23:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&n);
     ~~~~~^~~~~~~~~
foo.cc: In function 'int main()':
foo.cc:39:10: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d",&n);
     ~~~~~^~~~~~~~~

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