View Compilation Error

0_0_9902079_18382.cpp: In function `int main()':
0_0_9902079_18382.cpp:15: error: `x' undeclared (first use this function)
0_0_9902079_18382.cpp:15: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_9902079_18382.cpp:31: error: `strrev' undeclared (first use this function)