Type conversion

In computer science, type conversion, type casting, type coercion, and type juggling are different ways of changing an expression from one data type to another. An example would be the conversion of an integer value into a floating point value or its textual representation as a string, and vice versa. Type conversions can take advantage of certain features of type hierarchies or data representations. Two important aspects of a type conversion are whether it happens implicitly (automatically) or explicitly, and whether the underlying data representation is converted from one representation into another, or a given representation is merely reinterpreted as the representation of another data type. In general, both primitive and compound data types can be converted.

Each programming language has its own rules on how types can be converted. Languages with strong typing typically do little implicit conversion and discourage the reinterpretation of representations, while languages with weak typing perform many implicit conversions between data types. Weak typing language often allow forcing the compiler to arbitrarily interpret a data item as having different representations—this can be a non-obvious programming error, or a technical method to directly deal with underlying hardware.

In most languages, the word coercion is used to denote an implicit conversion, either during compilation or during run time. For example, in an expression mixing integer and floating point numbers (like 5 + 0.1), the compiler will automatically convert integer representation into floating point representation so fractions are not lost.