View Compilation Error

0_0_6313759_11973.cpp: In function `int main()':
0_0_6313759_11973.cpp:12: error: `f' undeclared (first use this function)
0_0_6313759_11973.cpp:12: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_6313759_11973.cpp:12: error: expected `;' before "while"