View Compilation Error

0_0_7928723_4712.cpp: In function `int main()':
0_0_7928723_4712.cpp:28: error: `mark' undeclared (first use this function)
0_0_7928723_4712.cpp:28: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_7928723_4712.cpp:29: error: `mark1' undeclared (first use this function)