View Compilation Error

0_0_4846325_19155.cpp: In function `int plus(int)':
0_0_4846325_19155.cpp:8: error: `plus' undeclared (first use this function)
0_0_4846325_19155.cpp:8: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_4846325_19155.cpp: At global scope:
0_0_4846325_19155.cpp:11: error: `main' must return `int'
0_0_4846325_19155.cpp: In function `int main(...)':
0_0_4846325_19155.cpp:16: error: `plus' undeclared (first use this function)