Introduction to Modern Fortran: Key Points

A Trivial Program

Fortran programs start with the program <label> statement.
Fortran programs end with the end program <label> statement.
Always use implicit none to prevent implicit typing for variables.
Fortran comments start with !.
The -o flag specifies the name of the compiled executable: <compiler_command> -o <executable_name> <source_file.f90>.

There are 5 intrinsic data types for Fortran variables: integer, real, complex, logical, and character.
Fortran variables are declared with the syntax: <variable_type> :: <variable_name>
Assign a value to a variable with the syntax: <variable> = <value>
Never assign a value on the same line as a variable is declared. This gives the variable the save attribute.
Parameters are variables whose value can’t be changed: <variable_type>, parameter :: <variable_name> = <variable_value>.

Operators in order of precedance: **, *, /, +, and -.
List of intrinsic maths functions.
A numeric variables kind specifies its floating-point precision. 32-bit, 64-bit etc.
Always specify a kind when defining and assigning values to variables. Otherwise Fortran will default to the compilers single precision.
Avoid mixing precision and kinds (e.g. integers with reals, or 32-bit with 64-bit). The compiler will implicitly convert the lower precision value to a higher precision value. This can slow down your programs.