foo.cc:9:5: error: 'int iszero' redeclared as different kind of entity
    9 | int iszero=0;
      |     ^~~~~~
In file included from /usr/include/c++/9/cmath:45,
                 from /usr/include/x86_64-linux-gnu/c++/9/bits/stdc++.h:41,
                 from foo.cc:3:
/usr/include/math.h:1048:1: note: previous declaration 'template<class __T> bool iszero(__T)'
 1048 | iszero (__T __val)
      | ^~~~~~
foo.cc: In function 'int main()':
foo.cc:18:12: error: invalid operands of types '<unresolved overloaded function type>' and 'int' to binary 'operator>='
   18 |   if(iszero>=2)
      |      ~~~~~~^~~
foo.cc:31:11: error: no post-increment operator for type
   31 |     iszero++;
      |           ^~

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