View Compilation Error

0_0_4902986_27906.cpp:4: error: `main' must return `int'
0_0_4902986_27906.cpp: In function `int main(...)':
0_0_4902986_27906.cpp:5: error: expected init-declarator before "sum"
0_0_4902986_27906.cpp:5: error: expected `,' or `;' before "sum"
0_0_4902986_27906.cpp:6: error: `b' undeclared (first use this function)
0_0_4902986_27906.cpp:6: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_4902986_27906.cpp:7: error: `sum' undeclared (first use this function)