View Compilation Error

0_0_10425988_2751.cpp: In function `int main()':
0_0_10425988_2751.cpp:9: error: `_int64' undeclared (first use this function)
0_0_10425988_2751.cpp:9: error: (Each undeclared identifier is reported only once for each function it appears in.)
0_0_10425988_2751.cpp:9: error: expected `;' before "a"
0_0_10425988_2751.cpp:11: error: `sum' undeclared (first use this function)
0_0_10425988_2751.cpp:16: error: `a' undeclared (first use this function)