foo.c:2:1: error: unknown type name 'using'
    2 | using namespace std;
      | ^~~~~
foo.c:2:17: error: expected '=', ',', ';', 'asm' or '__attribute__' before 'std'
    2 | using namespace std;
      |                 ^~~
foo.c: In function 'main':
foo.c:16:27: warning: implicit declaration of function 'upper_bound' [-Wimplicit-function-declaration]
   16 |                         a[upper_bound(a+1,a+top,x)-a]=x;
      |                           ^~~~~~~~~~~
foo.c:16:51: error: invalid operands to binary - (have 'int' and 'int *')
   16 |                         a[upper_bound(a+1,a+top,x)-a]=x;
      |                           ~~~~~~~~~~~~~~~~~~~~~~~~^
      |                           |                       |
      |                           int                     int *

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