View Compilation Error

0_0_6470168_31214.c:4: error: syntax error before "is_used"
0_0_6470168_31214.c:5: error: syntax error before "xx"
0_0_6470168_31214.c: In function `main':
0_0_6470168_31214.c:9: error: `bool' undeclared (first use in this function)
0_0_6470168_31214.c:9: error: (Each undeclared identifier is reported only once
0_0_6470168_31214.c:9: error: for each function it appears in.)
0_0_6470168_31214.c:9: error: syntax error before "flag"
0_0_6470168_31214.c:11: error: `flag' undeclared (first use in this function)
0_0_6470168_31214.c:14: error: `false' undeclared (first use in this function)
0_0_6470168_31214.c:25: error: `true' undeclared (first use in this function)
0_0_6470168_31214.c:42: error: syntax error before '/' token