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@ -1,21 +1,21 @@
[#]: collector: (lujun9972)
[#]: translator: ( )
[#]: reviewer: ( )
[#]: publisher: ( )
[#]: url: ( )
[#]: subject: (Start programming in Racket by writing a "guess the number" game)
[#]: via: (https://opensource.com/article/21/1/racket-guess-number)
[#]: author: (Cristiano L. Fontana https://opensource.com/users/cristianofontana)
[#]: subject: "Start programming in Racket by writing a "guess the number" game"
[#]: via: "https://opensource.com/article/21/1/racket-guess-number"
[#]: author: "Cristiano L. Fontana https://opensource.com/users/cristianofontana"
[#]: collector: "lkxed"
[#]: translator: " "
[#]: reviewer: " "
[#]: publisher: " "
[#]: url: " "
Start programming in Racket by writing a "guess the number" game
======
Racket is a great way to learn a language from the Scheme and Lisp
families.
Racket is a great way to learn a language from the Scheme and Lisp families.
![Person using a laptop][1]
I am a big advocate of learning multiple programming languages. That's mostly because I tend to get bored with the languages I use the most. It also teaches me new and interesting ways to approach programming.
Writing the same program in multiple languages is a good way to learn their differences and similarities. Previously, I wrote articles showing the same sample data plotting program written in [C & C++][2], JavaScript with [Node.js][3], and [Python and Octave][4].
Writing the same program in multiple languages is a good way to learn their differences and similarities. Previously, I wrote articles showing the same sample data plotting program written in [C & C++][2], JavaScript with [Node.js][3], and [Python and Octave][4].
This article is part of another series about writing a "guess the number" game in different programming languages. In this game, the computer picks a number between one and 100 and asks you to guess it. The program loops until you make a correct guess.
@ -31,7 +31,6 @@ When I start learning a new language, I usually look for a tutorial that introdu
Starting with Racket makes sense because it is very mature and versatile, and the community is very active. Since Racket is a Lisp-like language, a major characteristic is that it uses the [prefix notation][9] and a [lot of parentheses][10]. Functions and operators are applied to a list of operands by prefixing them:
```
(function-name operand operand ...)
@ -58,15 +57,14 @@ The major Linux distributions offer packaged versions of Racket, so [installatio
Here is a version of the "guess the number" program written in Racket:
```
#lang racket
(define (inquire-user number)
  (display "Insert a number: ")
  (define guess (string->number (read-line)))
  (cond [(> number guess) (displayln "Too low") (inquire-user number)]
        [(< number guess) (displayln "Too high") (inquire-user number)]
  (define guess (string->number (read-line)))
  (cond [(> number guess) (displayln "Too low") (inquire-user number)]
        [(< number guess) (displayln "Too high") (inquire-user number)]
        [else (displayln "Correct!")]))
(displayln "Guess a number between 1 and 100")
@ -75,14 +73,12 @@ Here is a version of the "guess the number" program written in Racket:
Save this listing to a file called `guess.rkt` and run it:
```
`$ racket guess.rkt`
$ racket guess.rkt
```
Here is some example output:
```
Guess a number between 1 and 100
Insert a number: 90
@ -111,9 +107,9 @@ Now for the next line. `(define ...)` is used to declare new variables or functi
This function recursively calls itself to repeat the question until the user guesses the right number. Note that I am not using loops; I feel that Racket programmers do not like loops and only use recursive functions. This approach is idiomatic to Racket, but if you prefer, [loops are an option][18].
The first step of the `inquire-user` function asks the user to insert a number by writing that string to the console. Then it defines a variable called `guess` that contains whatever the user entered. The [`read-line` function][19] returns the user input as a string. The string is then converted to a number with the [`string->number` function][20]. After the variable definition, the [`cond` function][21] accepts a series of conditions. If a condition is satisfied, it executes the code inside that condition. These conditions, `(> number guess)` and `(< number guess)`, are followed by two functions: a `displayln` that gives clues to the user and a `inquire-user` call. The function calls itself again when the user does not guess the right number. The `else` clause executes when the two conditions are not met, i.e., the user enters the correct number. The program's guts are this `inquire-user` function.
The first step of the `inquire-user` function asks the user to insert a number by writing that string to the console. Then it defines a variable called `guess` that contains whatever the user entered. The [read-line function][19] returns the user input as a string. The string is then converted to a number with the [string->number function][20]. After the variable definition, the [cond function][21] accepts a series of conditions. If a condition is satisfied, it executes the code inside that condition. These conditions, `(> number guess)` and `(< number guess)`, are followed by two functions: a `displayln` that gives clues to the user and a `inquire-user` call. The function calls itself again when the user does not guess the right number. The `else` clause executes when the two conditions are not met, i.e., the user enters the correct number. The program's guts are this `inquire-user` function.
However, the function still needs to be called! First, the program asks the user to guess a number between 1 and 100, and then it calls the `inquire-user` function with a random number. The random number is generated with the [`random` function][22]. You need to inform the function that you want to generate a number between 1 and 100, but the `random` function generates integer numbers up to `max-1`, so I used 101.
However, the function still needs to be called! First, the program asks the user to guess a number between 1 and 100, and then it calls the `inquire-user` function with a random number. The random number is generated with the [random function][22]. You need to inform the function that you want to generate a number between 1 and 100, but the `random` function generates integer numbers up to `max-1`, so I used 101.
### Try Racket
@ -124,15 +120,15 @@ Learning new languages is fun! I am a big advocate of programming languages poly
via: https://opensource.com/article/21/1/racket-guess-number
作者：[Cristiano L. Fontana][a]
选题：[lujun9972][b]
选题：[lkxed][b]
译者：[译者ID](https://github.com/译者ID)
校对：[校对者ID](https://github.com/校对者ID)
本文由 [LCTT](https://github.com/LCTT/TranslateProject) 原创编译，[Linux中国](https://linux.cn/) 荣誉推出
[a]: https://opensource.com/users/cristianofontana
[b]: https://github.com/lujun9972
[1]: https://opensource.com/sites/default/files/styles/image-full-size/public/lead-images/laptop_screen_desk_work_chat_text.png?itok=UXqIDRDD (Person using a laptop)
[b]: https://github.com/lkxed
[1]: https://opensource.com/sites/default/files/lead-images/laptop_screen_desk_work_chat_text.png
[2]: https://opensource.com/article/20/2/c-data-science
[3]: https://opensource.com/article/20/6/data-science-nodejs
[4]: https://opensource.com/article/20/2/python-gnu-octave-data-science