Some conditions will always be true or false dependent on the type that has been used. For instance, a signed char is never larger than 128 or an unsigned integer can never be negative (see the example below).

Example:

unsigned int z = 0;
...
if (z < 0) /* 'z' can never be < 0 */
{
... 
}
...

Any statements dependent on this test will never be executed.