View Compilation Error

548462_0_0_29857.c: In function `main':
548462_0_0_29857.c:22: error: `f' undeclared (first use in this function)
548462_0_0_29857.c:22: error: (Each undeclared identifier is reported only once
548462_0_0_29857.c:22: error: for each function it appears in.)