View Compilation Error

0_0_20331999_12341.cpp: In function 'int main()':
0_0_20331999_12341.cpp:69:21: error: 'sum' was not declared in this scope
                     sum-=num/2;
                     ^
0_0_20331999_12341.cpp:71:21: error: 'sum' was not declared in this scope
                     sum-=(num+1)/2;
                     ^