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Null pointer. In computing, a null pointer or null reference is a value saved for indicating that the pointer or reference does not refer to a valid object. Programs routinely use null pointers to represent conditions such as the end of a list of unknown length or the failure to perform some action; this use of null pointers can be compared to ...
The void type, in several programming languages derived from C and Algol68, is the return type of a function that returns normally, but does not provide a result value to its caller. Usually such functions are called for their side effects, such as performing some task or writing to their output parameters. The usage of the void type in such ...
The number of elements of the empty set (i.e., its cardinality) is zero. The empty set is the only set with either of these properties. For any set A : The empty set is a subset of A. The union of A with the empty set is A. The intersection of A with the empty set is the empty set. The Cartesian product of A and the empty set is the empty set.
Void pointers (void *) point to objects of unspecified type, and can therefore be used as "generic" data pointers. Since the size and type of the pointed-to object is not known, void pointers cannot be dereferenced, nor is pointer arithmetic on them allowed, although they can easily be (and in many contexts implicitly are) converted to and from ...
Undefined behavior. In computer programming, undefined behavior ( UB) is the result of executing a program whose behavior is prescribed to be unpredictable, in the language specification to which the computer code adheres. This is different from unspecified behavior, for which the language specification does not prescribe a result, and ...
The unit type is the terminal object in the category of types and typed functions. It should not be confused with the zero or empty type, which allows no values and is the initial object in this category. Similarly, the Boolean is the type with two values. The unit type is implemented in most functional programming languages.
Division by zero. The reciprocal function y = 1 x. As x approaches zero from the right, y tends to positive infinity. As x approaches zero from the left, y tends to negative infinity. In mathematics, division by zero, division where the divisor (denominator) is zero, is a unique and problematic special case. Using fraction notation, the general ...
The final value of k is undefined. The answer that it must be 10 assumes that it started at zero, which may or may not be true. Note that in the example, the variable i is initialized to zero by the first clause of the for statement. Another example can be when dealing with structs.