Memcache::increment() increments value of the item on the specified value. If item with key key was not numeric and cannot be converted to number, it will change it's value to value.
Parameter value is optional. It's default value is 1.
Note: Do not use Memcache::increment() with item, which was stored compressed, because consequent call to Memcache::get() will fail.
Also you can use memcache_increment() function. See example below.
Memcache::increment() returns new item's value on success or FALSE on failure.
Memcache::increment() does not create an item if it didn't exist.
See also Memcache::decrement(), Memcache::replace().