Each of the Following Lines of Code Purport to Round

Each of the following lines of code purport to round the results of the division of doubles to the nearest integer value (but still of type double).All are correct C++ code but some do not round correctly.Tell which rounds down,up,or to the nearest integer value,or is not reasonable
Assume that math.h has been included,and that all variables have appropriate values.
double x,y,z;
a)z = ceil(x/y);
b)z = ceil(x/y-0.5);
c)z = floor(x/y-0.5);
d)z = floor(x/y+0.5);
e)z = floor(x/y);