跟读练习: What's an if statement? 🤔 - 通过视频学习英语口语
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All right guys, we are on if statements.
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With an if statement, you do something if a condition you set is true.
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If not, then don't do it.
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It's as simple as that.
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We'll ask a user what their age is.
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If their age is greater than or equal to 18, they'll be allowed into our site.
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If they're under 18, well, we won't let them in.
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Let's declare variable age.
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Int age.
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Then we'll create a prompt.
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standard output enter your age.
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Standard input age.
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Okay, this is how to write an if statement.
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You type if, then a set of parentheses, then a set of curly braces.
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If some condition within the parentheses is true, you perform some subset of code.
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We are going to check if age is greater than or equal to 18.
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Greater than or equal to is a comparison operator.
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There's other comparison operators such as less than or equals to, less than, greater than.
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If you need to compare if two values are equal, you use two equal signs.
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You don't wanna say equals because then you're setting age equal to 18.
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Equals is the assignment operator.
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So let's check to see if age is greater than or equal to 18.
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Then we'll print a message.
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Standard output.
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Welcome to the site.
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Okay, let's Let's try this.
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Enter your age.
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Let's say that I'm 12.
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Well, it doesn't do anything.
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Since this condition evaluated to be false, we skip over this body of code.
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If it were true, then we execute it.
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This time my age is 21.
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I hit enter.
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Welcome to the site.
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If you would rather do something else if a condition is false, you can use an else statement.
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An else statement you will place at the end.
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There is no condition.
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Else, we will print standard output.
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You are not old enough to enter.
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Okay, let's try this again.
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Enter your age.
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I'll say that I'm 12.
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You are not old enough to enter.
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That's an if statement.
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If some condition is true, you do something.
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If not, you can do something else or nothing at all.
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There are more conditions you can check by using an else if statement.
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We can check another condition by adding else if.
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If this condition is false, check this else if condition.
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Let's check to see if age is less than zero.
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That means somebody hasn't been born yet.
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You haven't been born yet.
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Okay, now check this out.
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Let's say that my age is negative 10.
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Then I hit enter.
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You haven't been born yet.
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Since this condition was false, we skip this section of code.
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Then we check the else if statement.
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Since this condition was true, we execute this body of code.
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Then skip over the else statement.
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Let's add one more else if statement.
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Else if...
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Age is greater than or equal to 100.
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Standard.
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Output.
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You are too old to enter this site.
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Okay, enter your age.
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I am 120 years old.
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I hit enter.
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Welcome to the site.
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We check these conditions one by one starting from the top.
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We stated that our age was 120 years old.
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Even though we were expecting to execute this body of code, we instead executed this body of code within the if statement.
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That's because our age was technically still greater than or equal to 18.
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So the order of your if and else if statements does matter.
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It makes a difference.
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If we need to execute this body of code, if somebody's age is greater than or equal to 100, well then we should probably move that to the top.
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Then turn it into an if statement.
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Else if age is greater than or equal to 18, we will display this message.
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Let's try this one more time.
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Enter your age.
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I am 120 years old.
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I hit enter.
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You are too old to enter this site.
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So yeah, that's an if statement.
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You do something if a condition is true.
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If not, then you don't do it.
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If you would rather do something else, you can use an else statement.
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If there's other conditions you would like to check before reaching the else statement, you can use an else if statement.
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And there's really no limit to these.
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If you would like a copy of this code, I'll post this in the comment section down below.
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And well, yeah, those are if statements in C++.
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本课的词汇与口语要点
这节 B1 级别的口语课以视频“What's an if statement? 🤔”为素材。 视频中反复出现的词有：statement, condition, equal, enter, greater。 这段视频共有 92 个句子、733 个单词可供跟读。 讲话部分时长为 4:53。 说话人语速自然，每分钟约 150 个词，接近日常对话。 92% 的单词属于英语最常用的 3,000 词，词汇容易理解。
视频中的重点词汇
视频中最难的 10 个单词，附发音和释义：
| 单词 | 发音 | 释义 |
|---|---|---|
| execute 动词 | /ˈɛksɪˌkjuːt/ | 處決 /处决, 處死 /处死 |
| skip 动词 | /skɪp/ | 跳 |
| operator 名词 | /ˈɑpəˌɹeɪtɚ/ | 話務員 /话务员, 接線員 /接线员 |
| parenthesis 名词 | /pəˈɹɛn.θə.sɪs/ | 圓括號 /圆括号, 插入語 /插入语 |
| subset 名词 | /ˈsʌbˌsɛt/ | 子集 |
| curly 形容词 | /ˈkɝli/ | 捲曲的 /卷曲的 |
| evaluate 动词 | /ɪˈvaljʊeɪt/ | 評價 /评价 |
| declare 动词 | /dɪˈklɛɚ/ | 宣布 |
| technically 副词 | /ˈtɛk.nɪˌkəl.i/ | 嚴格來說 /严格来说 |
| assignment 名词 | /əˈsaɪn.mənt/ | 分配, 布置 |
值得反复跟读的句子
视频中简短而完整的句子，可以直接用在日常对话里：
- We'll ask a user what their age is.
- Then we'll create a prompt.
- Then we'll print a message.
- You haven't been born yet.
- Let's add one more else if statement.
视频中的语法
说话人最常用的结构，并附上视频中的原话：
| 结构 | 视频中的用法 |
|---|---|
| 条件句 if + 从句，will/would + 动词 — 条件及其结果 | If they're under 18, well, we won't let · If there's other conditions you would like |
| 被动语态 be + 过去分词 — 强调发生了什么，而不是谁做的 | be allowed · been born |
| 现在完成时 have/has + 过去分词 — 过去发生但与现在仍有关联的事 | hasn't been born · haven't been born |
| 比较级 -er than / more … than — 比较两个事物 | greater than |
需要注意的发音
说话人用了 19 次缩略和弱读形式，例如 don't, we'll, haven't。请按听到的简短形式来说。
- 长单词——注意重音位置: operator /ˈɑpəˌɹeɪtɚ/, parenthesis /pəˈɹɛn.θə.sɪs/, technically /ˈtɛk.nɪˌkəl.i/
中文母语者容易读错的音：
- /v/ — 不要读成 /w/，上齿轻触下唇: evaluate /ɪˈvaljʊeɪt/, variable [ˈvæɹ.i.ə.bl̩]
- 词尾辅音 — 要读清楚，后面不要加元音: execute /ˈɛksɪˌkjuːt/, skip /skɪp/, parenthesis /pəˈɹɛn.θə.sɪs/, subset /ˈsʌbˌsɛt/, brace /bɹeɪs/
如何用这段视频练习
- 先完整听一遍视频，不要开口，记下不认识的单词。
- 先用 0.75 倍速逐句跟读，熟练之后再回到正常速度。
- 录下自己的声音并与原声对比，特别注意 execute, skip, operator 这类单词。
什么是跟读法？
跟读法 (Shadowing) 是一种有科学依据的语言学习技巧，最初开发用于专业口译员的培训，并由多语言者Alexander Arguelles博士普及。这个方法简单而强大：您在听英语母语原声的同时立即大声重复——就像是一个延迟1-2秒紧跟说话者的影子。与被动听力或语法练习不同，跟读法强迫您的大脑和口腔肌肉同时处理并模仿真实的讲话模式。研究表明它能显着提高发音准确性，语调，节奏，连读，听力理解和口语流利度——使其成为雅思口语备考和真实英语交流最有效的方法之一。