View Compilation Error

0_0_8952369_24290.cpp:3: error: `set' does not name a type
0_0_8952369_24290.cpp: In function `int main()':
0_0_8952369_24290.cpp:8: error: `a' undeclared (first use this function)
0_0_8952369_24290.cpp:8: error: (Each undeclared identifier is reported only once for each function it appears in.)