View Compilation Error

0_0_31073686_13276.cpp: In function 'int main()':
0_0_31073686_13276.cpp:16:21: error: 'sum' was not declared in this scope
                     sum=sum+b;
                     ^
0_0_31073686_13276.cpp:18:35: error: 'sum' was not declared in this scope
                             cout<<sum;
                                   ^