foo.cc: In function 'int main()':
foo.cc:10:31: warning: suggest parentheses around '-' inside '<<' [-Wparentheses]
     fprintf(fp,"%s",~(1<<(n+1)-1));
                          ~~~~~^~
foo.cc:10:34: warning: format '%s' expects argument of type 'char*', but argument 3 has type 'int' [-Wformat=]
     fprintf(fp,"%s",~(1<<(n+1)-1));
                     ~~~~~~~~~~~~~^

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