如何从非空字符串（DrRacket）中提取最后一个字符。希望得到帮助 [英] How do you extract the last character from a non-empty string (DrRacket). Hope for assistance

问题描述

我对Scheme很新，我正在使用DrRacket，我希望得到一些急需的帮助。



我的第一个任务是提取第一个来自非空字符串的字符，我成功地这样做了。



;;签名：字符串优先：字符串 - > string

;;目的：从非空字符串中提取第一个字符

;;测试

（check-expect（string-第一个cookies）c）

（check-expect（字符串优先聚会）p）

;;定义：string-first

（define（string-first str）

（string-ith str 0））



现在，我是负责从非空字符串中提取最后一个字符。我无法弄清楚这一点。我的猜测是它涉及字符串长度与string-ith相结合。



希望有人可以帮助我。提前谢谢。

解决方案

阅读文档有什么问题？请参阅：

http：/ /sicp.ai.mit.edu/Fall-2004/manuals/scheme-7.5.5/doc/scheme_7.html [ ^ ]。



找到过程：过程：string-ref string k 。指数从零开始，因此您需要索引 length - 1 。另请参阅过程 string-length string 。

-SA

I'm fairly new to Scheme and I'm using DrRacket and I hope to get some much needed assistance.

I was first tasked to extract the first character from a non-empty string, which I was successful in doing so.

;;Signature: string-first: string -> string
;;Purpose: To extract the first character from a non-empty string
;;Tests
(check-expect (string-first "cookies") "c")
(check-expect (string-first "party") "p")
;;Definition: string-first
(define (string-first str)
(string-ith str 0))

Now, I am tasked with extracting the last character from a non-empty string. I cannot figure this out. My guess is that it involves "string-length" in combination with "string-ith."

Hopefully someone can help me out. Thank you in advance.

解决方案

What's wrong with just reading the documentation? Please see:
http://sicp.ai.mit.edu/Fall-2004/manuals/scheme-7.5.5/doc/scheme_7.html[^].

Locate the procedure: "procedure: string-ref string k". Indices are zero-based, so you need the index length − 1. Also see the procedure "string-length string".

—SA

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