View Compilation Error

0_0_9023300_6245.cpp: In function `int main()':
0_0_9023300_6245.cpp:58: error: `mod' undeclared (first use this function)
0_0_9023300_6245.cpp:58: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_9023300_6245.cpp: In function `void tree_down(int, int, int, lin*)':
0_0_9023300_6245.cpp:168: error: `mod' undeclared (first use this function)
0_0_9023300_6245.cpp: In function `int mod(int)':
0_0_9023300_6245.cpp:188: error: `int mod(int)' used prior to declaration