The "k < 0" means to run the for-loop while k is less then zero. In other words, that loop is not executed.
// for (int k = 4; k < 0; k--) // bad
for (int k = 4; k>=0; k--) // good
The "k < 0" means to run the for-loop while k is less then zero. In other words, that loop is not executed.
// for (int k = 4; k < 0; k--) // bad
for (int k = 4; k>=0; k--) // good