What Is Data Type in Fortran?


Angela Bailey

What Is Data Type in Fortran?

In Fortran, data types are used to define the kind of data that a variable can hold. Each variable in Fortran is associated with a specific data type, which determines the size and layout of the variable’s memory and the range of values that can be stored in it.

Basic Data Types

Fortran provides several basic data types:

  • Integer: Used to store whole numbers, both positive and negative. In Fortran, integers can have different sizes depending on the implementation, such as integer(2), integer(4), or integer(8).
  • Real: Used to store floating-point numbers with a decimal part. Real numbers can also have different sizes like real(4), real(8), or real(16).
  • Complex: Used to store complex numbers with both real and imaginary parts. Complex numbers can have different sizes like complex(4), complex(8), or complex(16).
  • Logical: Used to store boolean values, either true or false.
  • Character: Used to store text or strings of characters.

Detailed Explanation

The choice of data type depends on the kind of values that need to be stored and the precision required for calculations. For example, if you are working with large numbers that require high precision, you would choose a larger integer or real data type.

Fortran also provides derived data types, which are created by combining basic data types. These derived data types include structures, arrays, and pointers. Structures allow you to group related variables together, while arrays allow you to store multiple values of the same type in a single variable.

Pointers are used to store memory addresses.

Declaration and Initialization

In Fortran, variables need to be declared before they can be used. The declaration specifies the name of the variable and its data type. Variables can be initialized at the time of declaration or later in the program.

For example:

integer :: age
real(8) :: temperature = 98.6
character(len=10) :: name = 'John Doe'
logical :: is_valid = .true. 

In this example, we declare an integer variable age, a real variable temperature initialized with the value 98.6, a character variable name initialized with the string ‘John Doe’, and a logical variable is_valid initialized with the value true.

Type Casting

In Fortran, you can convert values from one data type to another using type casting. Type casting allows you to change the interpretation of a value without changing its representation in memory.

To perform type casting in Fortran, you can use built-in functions like int(), nint(), dble(), or cplx(). These functions convert values between different numeric types and handle rounding or truncation if necessary.


Data types in Fortran play a crucial role in defining the kind of data that can be stored in variables. By choosing the appropriate data type, you can ensure efficient memory usage and accurate calculations in your Fortran programs. Understanding the different data types and their characteristics is essential for writing robust and reliable code.

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