program circle real r, area c This program reads a real number r and prints c the area of a circle with radius r. write (*,*) 'Give radius r:' read (*,*) r area = 3.14159*r*r write (*,*) 'Area = ', area stop endThe lines that begin with with a "c" are comments and has no purpose other than to make the program more readable for humans. Originally, all Fortran programs had to be written in all upper-case letters. Most people now write lower-case since this is more legible, and so will we.
program name declarations statements stop endIn this tutorial, words that are in italics should not be taken as literal text, but rather as a generic description. The stop statement is optional and may seem superfluous since the program will stop when it reaches the end anyways, but it is recommended to always terminate a program with the stop statement to emphasize that the execution flow stops there.
Col. 1 : Blank, or a "c" or "*" for comments Col. 2-5 : Statement label (optional) Col. 6 : Continuation of previous line (optional) Col. 7-72 : Statements Col. 73-80: Sequence number (optional, rarely used today)Most lines in a Fortran 77 program starts with 6 blanks and ends before column 72, i.e. only the statement field is used. Note that Fortran 90 allows free format.
c23456789 (This demonstrates column position!) c The next statement goes over two physical lines area = 3.14159265358979 + * r * rAny character can be used instead of the plus sign as a continuation character. It is considered good programming style to use either the plus sign, an ampersand, or numbers (2 for the second line, 3 for the third, and so on).
c23456789 (This demonstrates column position!) programme cc integer int int = 12 write(*,*) 'The value of int is', + int end stop