View Compilation Error

0_0_12068666_5531.cpp: In function `int main()':
0_0_12068666_5531.cpp:8: error: `sum' undeclared (first use this function)
0_0_12068666_5531.cpp:8: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_12068666_5531.cpp: In function `int sum(int)':
0_0_12068666_5531.cpp:13: error: `int sum(int)' used prior to declaration