Ruby中的条件语句

太过爱你忘了你带给我的痛 2023-03-05 09:56 23阅读 0赞

## Ruby条件语句 **(**Ruby conditional statements**)** ##

**Conditional statements** are also known by the name of **conditional processing or conditional expressions**. They are used to perform a certain set of instructions if a specified condition is met. The conditions are generally of Boolean type and return either true or false as the result. Conditionals are formed using if or case with some comparison operators. A conditional assists data about where to move next. In Ruby, 0 is considered as true whereas in other programming languages it is considered false.

**条件语句**也称为**条件处理或条件表达式**的名称。 如果满足指定条件，它们将用于执行一组特定的指令。 条件通常为布尔类型，并且返回true或false作为结果。 使用if或case以及一些比较运算符来形成条件。 关于下一步移动位置的条件辅助数据。 在Ruby中，0被视为true，而在其他编程语言中，其被视为false。

Following are the **basic type of conditional statements** which are supported by Ruby:

以下是Ruby支持**的条件语句**的**基本类型** ：

1.  If statement
    
    如果声明
2.  If else statement
    
    如果另有陈述
3.  short if statement
    
    简短的if语句
4.  If else if statement
    
    如果不是，则声明
5.  Unless
    
    除非
6.  Case statement
    
    案例陈述

### 1)如果声明 **(**1) if statement**)** ###

It is the most basic type of branching statement you get to know during programing. In the simpler words, it means if you find this true, do something, and otherwise do something else. They are quite easy to write.

它是您在编程过程中了解的最基本的分支语句类型。 用简单的话来说，这意味着如果您发现这是正确的，请执行某项操作，否则执行其他操作。 它们很容易编写。

**Syntax:**

**句法：**

if (condition)
            #statements
        end

**Example:**

**例：**

puts "Enter your age"
    age = gets.chomp
    
    if age.to_i >= 18
    	puts "You are allowed to vote."
    end

**Output**

**输出量**

First run:
    Enter your age
    23
    You are allowed to vote.
    
    Second run:
    Enter your age
    12

### 2)if else语句 **(**2) if else statement**)** ###

**if else statement** is used to indicate what should happen next if the condition fails to be satisfied. It comes with an additional **'else'** with it.

**if else语句**用于指示如果条件不满足，接下来将发生什么。 它带有一个附加的**“ else”** 。

**Syntax:**

**句法：**

if (condition)
    	    #instructions
        else
    	    #instructions
        end

In the above, if..end example we can observe that nothing is showing to the user as the message if the user fails to be older than 18. Let us modify that code and informs the user by using else keyword.

在上面的if..end示例中，如果用户未超过18岁，我们可以观察到没有任何内容显示为消息。让我们修改该代码，并使用else关键字通知用户。

**Example:**

**例：**

puts "Enter your age"
    age = gets.chomp
    
    if age.to_i >= 18
    	puts "You are allowed to vote."
    else
    	puts "You are younger than 18 years."
    end

**Output**

**输出量**

First run:
    Enter your age 
    23 
    You are allowed to vote.
    
    Second run:
    Enter your age 
    12 
    You are younger than 18 years.

### 3)简短陈述 **(**3) Short-if statement**)** ###

Its functioning is very similar to if...else statement. It is a ternary operator and used for computing result just in one line which saves space and eventually reduces the line of code. It is recommended to be used in small tasks.

它的功能与if ... else语句非常相似。 它是三元运算符，仅用于一行计算结果，从而节省了空间并最终减少了代码行。 建议用于小型任务。

**Syntax:**

**句法：**

result = (condition) ? (expression-if-true) : (expression-if-false)

**Example:**

**例：**

puts "Enter marks:"
    marks = gets.chomp.to_i
    
    result = (marks>45)?'pass':'fail'
    
    puts "#{result}"

**Output**

**输出量**

First run:
    Enter marks: 
    67 
    pass
    
    Second run:
    Enter marks: 
    12 
    fail

In the above example, you have observed that we can compute the result in a single line and we are storing the result in a variable. It is also known as ?: operator.

在上面的示例中，您已经观察到我们可以在一行中计算结果，并且将结果存储在变量中。 也称为？：运算符。

### 4)if else if语句 **(**4) if else if statement**)** ###

The if-else if statement provides great help when you have more than two conditions. If the if condition is evaluated as false then the pointer will jump to elsif condition and so on. Remember that, in syntax, it is elsif (an else without 'e').

如果您有两个以上条件，则if-else if语句将提供很大的帮助。 如果if条件的值为假，则指针将跳转到elsif条件，依此类推。 请记住，在语法上，它是elsif (另一个没有'e'的)。

**Syntax:**

**句法：**

if expression
            #code block.
        elsif  expression2
            #code block.   
        elsif  expression3
            #code block.   
        else
            #code block
        end

**Example:**

**例：**

puts "Enter fruit:"
    fruit = gets.chomp
    
    if fruit=="banana"
    	puts "Outstanding Choice!"
    elsif fruit=="Apple"
    	puts "An Apple a day, keeps the doctor away!"
    elsif fruit=="Grapes"
    	puts "Good in taste"
    else
    	puts "I can't get you"
    end

**Output**

**输出量**

First run:
    Enter fruit:
    Grapes
    Good in taste
    
    Second run:
    Enter fruit:
    Apple
    An Apple a day, keeps the doctor away!

### 5)除非 **(**5) unless**)** ###

The unless statement is a converse of if statement. If statement is evaluated when the condition turns out to be true but in the case of unless statement, the code block it contains will only be executed when the condition results to be false.

除非语句与if语句相反。 如果条件为真时对if语句进行评估，但在nons语句的情况下，仅当条件为false时才执行其中包含的代码块。

**Syntax:**

**句法：**

unless condition
    	    #code block
        end

**Example (a):**

**范例(a)：**

flag = false
    
    unless flag
    	puts "flag is false"
    end

**Output**

**输出量**

flag is false

**Example (b):**

**范例(b)：**

flag = true
    
    unless flag
    	puts "flag is false"
    end

**Output**

**输出量**

Note: No output will be there because now flag is 'true'.

### 6)案例陈述 **(**6) case statement**)** ###

case statement can be interchangeably used with if..elsif..end statement. We use a keyword when for implementing case conditionals. Case statement makes our code more readable.

case语句可以与if..elsif..end语句互换使用。 在实现案例条件时 ，我们使用关键字。 案例陈述使我们的代码更具可读性。

**Syntax:**

**句法：**

case (variable name)
        when (condition)
            #statements
        when (condition)
            #statements
        else
            #statements
        end

**Example:**

**例：**

puts "Enter fruit:"
    fruit = gets.chomp
    
    case fruit
    when "Banana"
    	puts "Outstanding Choice!"
    when "Apple"
    	puts "An Apple a day, keeps the doctor away!"
    when "Grapes"
    	puts "Good in taste"
    else
    	puts "I can't get you"
    end

**Output**

**输出量**

First run:
    Enter fruit: 
    Banana 
    Outstanding Choice!
    
    Second run:
    Enter fruit: 
    Apple
    An Apple a day, keeps the doctor away!

Observe that we have implemented the same logic using case statement as we have done in if..elsif..end statement.

观察到，我们使用case语句实现了与if..elsif..end语句相同的逻辑。

> 翻译自: [https://www.includehelp.com/ruby/conditional-statements.aspx][https_www.includehelp.com_ruby_conditional-statements.aspx]

[https_www.includehelp.com_ruby_conditional-statements.aspx]: https://www.includehelp.com/ruby/conditional-statements.aspx