More specifically, your professor wants to know that you understand the concept of a logical bug (as opposed to a syntactic bug). The idea is that the program compiles, but does not produce the correct results.
An example: a program that is supposed to determine the maximum of 2 numbers input by the user, but instead outputs the minimum. The logical error is highlighted in red.
using namespace std;
int i1, i2, iMax;
cout << "Please insert your first number: ";
cin >> i1;
cout << endl << "Please insert your second number: ";
cin >> i2;
iMax = i1;
if (i2 < i1)
iMax = i2;
cout << endl << "The highest number was " << iMax << endl;