Fortran, with its emphasis on numerical operations, has four data types just for numbers. These are collectively known as the arithmetic data types. Arithmetic expressions can include mixtures of data types and, in most cases, automatic type conversions are provided. In other circumstances, however, especially in procedure calls, there is no provision for automatic type conversion and it is essential for data types to match exactly.
The range and precision of the arithmetic data types are not specified by the Standard: typical values are indicated below, but the only way to be sure is to check the manuals provided with your own Fortran system.
Several intrinsic functions are available to convert from one data type to another. Conversion from character strings to numbers and vice-versa can be complicated; these are best carried out with the internal file READ and WRITE statements (see section 10.3).
There are, as yet, no user-defined or structured data types in Fortran.