View Compilation Error

0_0_5922926_22750.cpp: In function `int main()':
0_0_5922926_22750.cpp:14: error: `ans' undeclared (first use this function)
0_0_5922926_22750.cpp:14: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_5922926_22750.cpp:15: error: `pre' undeclared (first use this function)
0_0_5922926_22750.cpp:17: error: `num' undeclared (first use this function)