Fortran/Fortran variables

Introduction
In programming, a variable is a container for data that the program can change. You typically declare variables before you use them to provide information on what kind of data they should store. However, Fortran allows variables to be created implicitly. Absent an  statement, undeclared variables and arguments beginning with  /  through  /  (the "in" group) will be , and all other undeclared variables and arguments will be.

Many consider using variables without declaring them bad practice. If you want to be forced to declare variables, code  first.

General Examples
Examples of usual variables are listed below The following does exactly the same thing, but in the shorter, more archaic form: If memory layout counts to you, note that m(1,1) is followed in memory by m(2,1), and not by m(1,2).

A variable can be set by placing it before an equal sign, which is followed by the value to which it is set. Given the declarations above, the following assignments are possible:

A variable can appear on both sides of an assignment. The right hand side is evaluated first, and the variable is then assigned to that value:

Variables can be converted from one type to another, but unlike in C++ or Java where you would typecast the variable, in Fortran you use the intrinsic procedures: Again, the same thing in the simpler, archaic form:

Declaration
One can declare arrays using two different notations. The following example illustrates the notations for arrays of  type and of length 5. For multidimensional arrays one needs to specify the length of each dimension. The following example highlights the case of a 5x6 integer matrix aka a two-dimensional array of length (5,6). (Again, showing both notations.)

Initialization
To initialize arrays with actual values one has multiple options: set specific elements, specific ranges, or the whole array. To set multidimensional arrays one need to make use of, and   commands. Fortran uses column-major ordering such that the upper example produces a often confusing matrix. For a row-major ordering one can use the following example which highlights the use of the order argument to specify along which dimension to sort first.