View Compilation Error

0_0_31073661_29763.cpp: In function 'int main()':
0_0_31073661_29763.cpp:15:17: error: 'sum' was not declared in this scope
                 sum=sum+b;
                 ^
0_0_31073661_29763.cpp:18:15: error: 'sum' was not declared in this scope
         cout<<sum;
               ^