View Compilation Error

916802_0_0_17890.c: In function `main':
916802_0_0_17890.c:7: error: `sum' undeclared (first use in this function)
916802_0_0_17890.c:7: error: (Each undeclared identifier is reported only once
916802_0_0_17890.c:7: error: for each function it appears in.)