View Compilation Error

23836_0_31047.c: In function `main':
23836_0_31047.c:15: error: `bool' undeclared (first use in this function)
23836_0_31047.c:15: error: (Each undeclared identifier is reported only once
23836_0_31047.c:15: error: for each function it appears in.)
23836_0_31047.c:15: error: syntax error before "flag"
23836_0_31047.c:35: error: `flag' undeclared (first use in this function)
23836_0_31047.c:35: error: `false' undeclared (first use in this function)
23836_0_31047.c:41: error: `true' undeclared (first use in this function)
xx