Ruby中的 条件表达式

IF 语句和unless语句

本质上，unless 与 if 的意思，刚好相反

#if条件语句
x = 10
y = 20

if x == y 
  puts "x is the same as y" 
else 
  puts "x and y are not the same" 
end

#if嵌套
if x == y 
  puts "x is equal to y" 
elsif x >= z 
  puts "x is greater than or equal to z" 
elsif x < z 
  puts "x is less than y" 
else 
  puts "Something else" 
end


#unless 条件语句（除非...）
players = ["Correa", "Carter", "Altuve"]
unless players.empty?
    players.each { |player| puts player}
end
#同上
players.each{ |player| puts player } unless players.empty?
players.each{ |player| puts player } if !players.empty?
players2 =[]
unless players2.empty?
    players2.each { |player| puts player}
end

The following is the list of arithmetic functions to use in a Ruby program:

+: 加法

-: 减法

/: 除法

*: 乘法

**: 乘方

你可以在这里看到一步一步的看到他的执行过程

5 + 15 * 20 - 2 / 6 ** 3 - (3 + 1)  # parenthesis
5 + 15 * 20 - 2 / 6**3 - 4          # exponents
5 + 15 * 20 - 2 / 216 - 4           # multiplication
5 + 300 - 2 / 216 - 4               # division
5 + 300 - 0 - 4                     # addition
305 - 0 - 4                         # subtraction
301

优先级的记忆PEMDAS Please Excuse My Dear Aunt Sally（请原谅我亲爱的萨莉阿姨），即:

• P: 括号
• E: 乘方
• M: 乘法
• D: 除法
• A: 加法
• S: 减法

关系运算符

>: Greater than
<: Less than
>=: Greater than or equal to
<=: Less than or equal to
!=: Not equal to