View Compilation Error

0_0_29102276_21136.cpp:2:11: error: '::main' must return 'int'
 void main()
           ^
0_0_29102276_21136.cpp: In function 'int main()':
0_0_29102276_21136.cpp:5:3: error: 'sum' was not declared in this scope
   sum=a+b;
   ^