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Xingyu.Wang
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[#]: collector: (lujun9972)
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[#]: translator: (unigeorge)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (Learn Fortran by writing a "guess the number" game)
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[#]: via: (https://opensource.com/article/21/1/fortran)
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[#]: author: (Jim Hall https://opensource.com/users/jim-hall)
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Learn Fortran by writing a "guess the number" game
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======
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Because Fortran was written in the punched card era, its syntax is
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pretty limited. But you can still write useful and interesting programs
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with it.
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![Person typing on a 1980's computer][1]
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The first compiled programming language I learned was Fortran 77. While growing up, I taught myself how to write programs in BASIC on the Apple II and later in QBasic on DOS. But when I went to university to study physics, I learned [Fortran][2].
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Fortran used to be quite common in scientific computing. And once upon a time, all computer systems had a Fortran compiler. Fortran used to be as ubiquitous as Python is today. So if you were a physics student like me, working in the 1990s, you learned Fortran.
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I always thought Fortran was somewhat similar to BASIC, so I quickly took to Fortran whenever I needed to write a quick program to analyze lab data or perform some other numerical analysis. And when I got bored, I wrote a "Guess the number" game in Fortran, where the computer picks a number between one and 100 and asks me to guess the number. The program loops until I guess correctly.
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The "Guess the number" program exercises several concepts in programming languages: how to assign values to variables, how to write statements, and how to perform conditional evaluation and loops. It's a great practical experiment for learning a new programming language.
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### The basics of Fortran programming
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While Fortran has been updated over the years, I am most familiar with Fortran 77, the implementation I learned years ago. Fortran was created when programmers wrote programs on punched cards, so "classic" Fortran is limited to the data you could put on a punched card. That means you could only write classic Fortran programs with these limitations:
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* Only one line of source code per card is allowed.
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* Only columns 1–72 are recognized (the last eight columns, 73-80, are reserved for the card sorter).
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* Line numbers ("labels") are in columns 1–5.
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* Program statements go in columns 7–72.
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* To continue a program line, enter a continuation character (usually `+`) in column 6.
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* To create a comment line, enter `C` or `*` in column 1.
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* Only the characters `A` to `Z` (uppercase), `0` to `9` (numbers), and the special characters `= + - * / ( ) , . $ ' :` and space are used.
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With these limitations, you can still write very useful and interesting programs.
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### Guess the number in Fortran
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Explore Fortran by writing the "Guess the number" game. This is my implementation:
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```
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CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
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C PROGRAM TO GUESS A NUMBER 1-100
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CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
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PROGRAM GUESSNUM
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INTEGER SEED, NUMBER, GUESS
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PRINT *, 'ENTER A RANDOM NUMBER SEED'
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READ *, SEED
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CALL SRAND(SEED)
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NUMBER = INT( RAND(0) * 100 + 1 )
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PRINT *, 'GUESS A NUMBER BETWEEN 1 AND 100'
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10 READ *, GUESS
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IF (GUESS.LT.NUMBER) THEN
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PRINT *, 'TOO LOW'
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ELSE IF (GUESS.GT.NUMBER) THEN
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PRINT *, 'TOO HIGH'
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ENDIF
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IF (GUESS.NE.NUMBER) GOTO 10
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PRINT *, 'THATS RIGHT!'
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END
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```
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If you are familiar with other programming languages, you can probably figure out what this program is doing by reading the source code. The first three lines are a comment block to indicate the program's function. The fourth line, `PROGRAM GUESSNUM`, identifies this as a program, and it is closed by the `END` statement on the last line.
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After defining a few variables, the program prompts the user to enter a random number seed. A Fortran program cannot initialize the random number generator from the operating system, so you must always start the random number generator with a "seed" value and the `SRAND` subroutine.
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Fortran generates random numbers between 0 and 0.999... with the `RAND(0)` function. The `0` value tells the `RAND` function to generate another random number. Multiply this random number by 100 to generate a number between 0 and 99.999…, and then add 1 to get a value between 1 and 100.999… The `INT` function truncates this to an integer; thus, the variable `NUMBER` is a random number between 1 and 100.
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The program prompts the user, then enters a loop. Fortran doesn't support the `while` or `do-while` loops available in more modern programming languages. Instead, you must construct your own using labels (line numbers) and `GOTO` statements. That's why the `READ` statement has a line number; you can jump to this label with the `GOTO` at the end of the loop.
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Punched cards did not have the `<` (less than) or `>` (greater than) symbols, so Fortran adopted a different syntax to compare values. To test if one value is less than another, use the `.LT.` (less than) comparison. To test if a value is greater than another, use `.GT.` (greater than). Equal and not equal are `.EQ.` and `.NE.`, respectively.
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In each iteration of the loop, the program tests the user's guess. If the user's guess is less than the random number, the program prints `TOO LOW`, and if the guess is greater than the random number, the program prints `TOO HIGH`. The loop continues until the user's guess is the same as the random number.
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When the loop exits, the program prints `THATS RIGHT!` and ends immediately.
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```
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$ gfortran -Wall -o guess guess.f
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$ ./guess
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ENTER A RANDOM NUMBER SEED
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93759
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GUESS A NUMBER BETWEEN 1 AND 100
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50
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TOO LOW
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80
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TOO HIGH
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60
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TOO LOW
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70
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TOO LOW
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75
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TOO HIGH
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73
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TOO LOW
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74
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THATS RIGHT!
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```
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Every time you run the program, the user needs to enter a different random number seed. If you always enter the same seed, the program will always pick the same random number.
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### Try it in other languages
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This "guess the number" game is a great introductory program when learning a new programming language because it exercises several common programming concepts in a pretty straightforward way. By implementing this simple game in different programming languages, you can demonstrate some core concepts and compare each language's details.
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Do you have a favorite programming language? How would you write the "guess the number" game in it? Follow this article series to see examples of other programming languages that might interest you.
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/1/fortran
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作者：[Jim Hall][a]
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选题：[lujun9972][b]
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译者：[unigeorge](https://github.com/unigeorge)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/jim-hall
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/1980s-computer-yearbook.png?itok=eGOYEKK- (Person typing on a 1980's computer)
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[2]: https://en.wikipedia.org/wiki/Fortran
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@ -0,0 +1,129 @@
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[#]: collector: (lujun9972)
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[#]: translator: (unigeorge)
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[#]: reviewer: ( )
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[#]: publisher: ( )
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[#]: url: ( )
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[#]: subject: (Learn Fortran by writing a "guess the number" game)
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[#]: via: (https://opensource.com/article/21/1/fortran)
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[#]: author: (Jim Hall https://opensource.com/users/jim-hall)
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通过写“猜数字”游戏学习 Fortran
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======
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Fortran 是在打孔卡时代编写的语言，因此它的语法非常有限。但你仍然可以用它编写有用和有趣的程序。
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![Person typing on a 1980's computer][1]
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Fortran 77 是我学习的第一门编译型编程语言。一开始时，我自学了如何在 Apple II 上用 BASIC 编写程序，后来又学会在 DOS 上用 QBasic 编写程序。但是当我去大学攻读物理学时，我又学习了 [Fortran][2]。
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Fortran 曾经在科学计算中很常见。曾几何时，所有计算机系统都有一个 Fortran 编译器。Fortran 曾经像今天的 Python 一样无处不在。因此，如果你是像我这样的物理学专业学生，在 1990 年代工作，那你肯定学习了 Fortran。
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我一直认为 Fortran 与 BASIC 有点相似，所以每当我需要编写一个简短程序，来分析实验室数据或执行其他一些数值分析时，我都会很快想到 Fortran。我在空闲时用 Fortran 编写了一个“猜数字”游戏，其中计算机会在 1 到 100 之间选择一个数字，并让我猜这个数字。程序会一直循环，直到我猜对了为止。
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“猜数字”程序练习了编程语言中的几个概念：如何为变量赋值、如何编写语句以及如何执行条件判断和循环。这是学习新编程语言时一个很好的的实践案例。
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### Fortran 编程基础
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虽然 Fortran 这些年来一直在更新，但我最熟悉的还是 Fortran 77，这是我多年前学习的实现版本。Fortran 是程序员还在打孔卡上编程的年代创建的，因此“经典”Fortran 仅限于处理可以放在打孔卡上的数据。这意味着你只能编写符合以下限制条件的经典 Fortran 程序（LCTT 译注：后来的 Fortran 95 等版本已经对这些限制做了很大的改进，如有兴趣**建议直接学习新版**）：
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* 每张卡只允许一行源代码。
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* 仅识别第 1-72 列（最后八列，73-80，保留给卡片分类器）。
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* 行号（“标签”）位于第 1-5 列。
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* 程序语句在第 7-72 列。
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* 要表示跨行，请在第 6 列中输入一个连续字符（通常是 `+`）。
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* 要创建注释行，请在第 1 列中输入 `C` 或 `*`。
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* 只有字符`A` 到`Z`（大写字母）、`0` 到`9`（数字）和特殊字符`= + - * / ( ) , . $ ' :` 和空格能够使用。
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虽然有这些限制，你仍然可以编写非常有用和有趣的程序。
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### 在 Fortran 中猜数字
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通过编写“猜数字”游戏来探索 Fortran。这是我的实现代码：
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```
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CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
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C PROGRAM TO GUESS A NUMBER 1-100
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CCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCCC
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PROGRAM GUESSNUM
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INTEGER SEED, NUMBER, GUESS
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PRINT *, 'ENTER A RANDOM NUMBER SEED'
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READ *, SEED
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CALL SRAND(SEED)
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NUMBER = INT( RAND(0) * 100 + 1 )
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PRINT *, 'GUESS A NUMBER BETWEEN 1 AND 100'
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10 READ *, GUESS
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IF (GUESS.LT.NUMBER) THEN
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PRINT *, 'TOO LOW'
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ELSE IF (GUESS.GT.NUMBER) THEN
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PRINT *, 'TOO HIGH'
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ENDIF
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IF (GUESS.NE.NUMBER) GOTO 10
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PRINT *, 'THATS RIGHT!'
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END
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```
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如果你熟悉其他编程语言，你大概可以通过阅读源代码来弄清楚这个程序在做什么。前三行是注释块，表示程序的功能。第四行 `PROGRAM GUESSNUM` 将其标识为一个 <ruby><rb>程序</rb><rt>program</rt></ruby>，并由最后一行的 `END` 语句关闭。
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定义变量后，程序会提示用户输入随机数种子。Fortran 程序无法从操作系统初始化随机数生成器，因此你必须始终使用“种子”值和 `SRAND` <ruby><rb>子程序</rb><rt>subroutine</rt></ruby> 启动随机数生成器。
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Fortran 使用 `RAND(0)` 函数生成 0 到 0.999…… 之间的随机数。参数 `0` 告诉 `RAND` 函数生成一个随机数。将此随机数乘以 100 以生成 0 到 99.999…… 之间的数字，然后加 1 得到 1 到 100.999…… 之间的值。`INT` 函数将结果截断为整数；因此，变量 `NUMBER` 就是一个介于 1 到 100 之间的随机数。
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程序会给出提示，然后进入一个循环。Fortran 不支持更现代的编程语言中可用的 `while` 或 `do-while` 循环（LCTT 译注：Fortran 95 等新版支持，也因此在一定程度上减少了 `GOTO` 的使用）。相反，你必须使用标签（行号）和 `GOTO` 语句来构建自己的循环。这就是 `READ` 语句有一个行号的原因：你可以在循环末尾使用 `GOTO` 跳转到此标签。
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穿孔卡片没有 `<`（小于）和 `>`（大于）符号，因此 Fortran 采用了另一种语法来进行值比较。要测试一个值是否小于另一个值，请使用 `.LT.`（小于）。要测试一个值是否大于另一个值，请使用 `.GT.`（大于）。等于和不等于分别是 `.EQ.` 和 `.NE.`。
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在每次循环中，程序都会验证用户的猜测值。如果用户的猜测值小于随机数，程序打印 `TOO LOW`，如果猜测大于随机数，程序打印 `TOO HIGH`。循环会一直持续，直到用户的猜测值等于目标随机数为止。
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当循环退出时，程序打印 `THATS RIGHT!` 并立即结束运行。
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```
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$ gfortran -Wall -o guess guess.f
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$ ./guess
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ENTER A RANDOM NUMBER SEED
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93759
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GUESS A NUMBER BETWEEN 1 AND 100
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50
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TOO LOW
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80
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TOO HIGH
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60
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TOO LOW
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70
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TOO LOW
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75
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TOO HIGH
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73
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TOO LOW
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74
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THATS RIGHT!
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```
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每次运行程序时，用户都需要输入不同的随机数种子。如果你总是输入相同的种子，程序给出的随机数也会一直不变。
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### 在其他语言中尝试
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在学习一门新的编程语言时，这个“猜数字”游戏是一个很好的入门程序，因为它以非常简单的方式练习了几个常见的编程概念。通过用不同的编程语言实现这个简单的游戏，你可以弄清一些核心概念以及比较每种语言的细节。
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你有最喜欢的编程语言吗？如何用你最喜欢的语言来编写“猜数字”游戏？跟随本系列文章来查看你可能感兴趣的其他编程语言示例吧。
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--------------------------------------------------------------------------------
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via: https://opensource.com/article/21/1/fortran
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作者：[Jim Hall][a]
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选题：[lujun9972][b]
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译者：[unigeorge](https://github.com/unigeorge)
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校对：[校对者ID](https://github.com/校对者ID)
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本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
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[a]: https://opensource.com/users/jim-hall
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[b]: https://github.com/lujun9972
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[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/1980s-computer-yearbook.png?itok=eGOYEKK- (Person typing on a 1980's computer)
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[2]: https://en.wikipedia.org/wiki/Fortran
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