View Compilation Error

0_0_8723688_16979.cpp: In function `int main()':
0_0_8723688_16979.cpp:80: error: `f' undeclared (first use this function)
0_0_8723688_16979.cpp:80: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_8723688_16979.cpp:80: error: expected `;' before "lag"